Dynamically switching queueing schemes for network switches

ABSTRACT

An example system includes a first network node, a second network node, and a third network node. The first network node is configured to generate a first optical subcarrier representing first data, and transmit the first optical subcarrier to the second network node. The second network node is configured to receive the first optical subcarrier from the first network node, generate a second optical subcarrier representing the first data, where the second optical subcarrier is different from the first optical subcarrier, and transmit the second optical subcarrier to the third network node.

TECHNICAL FIELD

This disclosure relates to transmitting and receiving data over acommunications network.

BACKGROUND

Computing devices can exchange information with one another using acommunications network. As an example, computing devices can beinterconnected to one another via one or more intermediary networkdevices (e.g., routers, hubs, switches, etc.) and network links (e.g.,electrically conductive cables, optical fiber, wireless networkinterfaces, etc.). The network devices receive data packets from one ormore source computing devices, and forward each of the data packets toits respective destination computing device. In some implementations,the communications network can be a local area network (LAN), such as anEthernet LAN.

SUMMARY

In an aspect, a system includes a first network switch and a pluralityof first server computers communicatively coupled to the first networkswitch. The first network switch includes a first transceiver. The firsttransceiver is configured to transmit data according to a first maximumthroughput. Each first server computer includes a respective secondtransceiver. Each second transceiver is configured to transmit dataaccording to a second maximum throughput. The first maximum throughputis greater than the second maximum throughput. The first network switchis configured to transmit, using the first transceiver according to thefirst maximum throughput, first data to each of the first servercomputers. The first data includes a plurality of first opticalsubcarriers. Each first optical subcarrier is associated with adifferent one of the first server computers. Each of the first servercomputers is configured to receive, using a respective one of the secondtransceivers, the first data from the first network switch, and extract,from the first data, a respective portion of the first data addressed tothe first server computer.

Implementations of this aspect can include one or more of the followingfeatures.

In some implementations, each of the first server computer can beconfigured to extract the respective portion of the first data addressedto the first server computer by extracting a portion of the first datafrom the first optical subcarrier associated with the sever computer.

In some implementations, the system can further include a second networkswitch including a third transceiver. The third transceiver can beconfigured to transmit data according to a third maximum throughput. Thesystem can include a plurality of the first network switches. Each firstnetwork switch can include a respective fourth transceiver. Each fourthtransceiver can be configured to transmit data according to a fourthmaximum throughput. The third maximum throughput can be greater than thefourth maximum throughput. The second network switch can be configuredto transmit, using the fourth transceiver according to the fourthmaximum throughput, second data to each of the first network switches.The second data can include a plurality of second optical subcarriers.Each second optical subcarrier can be associated with a different one ofthe first network switches. Each of the first network switches can beconfigured to receive, using a respective one of the fourthtransceivers, the second data from the second network switch, andextract, from the second data, a respective portion of the second dataaddressed to the first network switch.

In some implementations, each of the first network switches can beconfigured to extract the respective portion of the second datacorresponding to the first network switch by extracting a portion of thesecond data from the second optical subcarrier associated with the firstnetwork switch.

In some implementations, the second network switch can further includeone or more fifth transceivers. The second network switch can beconfigured transmit, receive or both transmit and receive third datafrom a wide area network using the one or more fifth transceivers.

In some implementations, at least one of the first network switches canbe a top of rack network switch.

In some implementations, the second network switch can be a core networkswitch.

In some implementations, at least one of the first server computers canbe configured to transmit, using the second transceiver, second data tothe first network switch according to the second maximum throughput. Thesecond data can include a second optical subcarrier. The second opticalsubcarrier can be associated with the first network switch.

In some implementations, the first data can be transmitted using thefirst transceiver of the first network switch to each of the secondreceivers of the first server computers.

In some implementations, the second data can be transmitted using thesecond transceiver of the at least one of the first server computers tothe first transceiver of the first network switch.

In another aspect, a method includes transmitting first data from afirst network switch to each of a plurality of first server computers.The first network switch includes a first transceiver. The firsttransceiver is configured to transmit data according to a first maximumthroughput. The plurality of first server computers is communicativelycoupled to the first network switch. Each first server computer includesa respective second transceiver. Each second transceiver is configuredto transmit data according to a second maximum throughput. The firstmaximum throughput is greater than the second maximum throughput. Thefirst data includes a plurality of first optical subcarriers. Each firstoptical subcarrier is associated with a different one of the firstserver computers. The method also includes receiving, by each of thefirst server computers using a respective one of the secondtransceivers, the first data from the first network switch, andextracting, by each of the first server computers from the first data, arespective portion of the first data addressed to the first servercomputer.

Implementations of this aspect can include one or more of the followingfeatures.

In some implementations, each of the first server computer can beconfigured to extract the respective portion of the first data addressedto the first server computer by extracting a portion of the first datafrom the first optical subcarrier associated with the sever computer.

In some implementations, a second network switch can include a thirdtransceiver. The third transceiver can be configured to transmit dataaccording to a third maximum throughput. Each first network switch of aplurality of network switches can include a respective fourthtransceiver. Each fourth transceiver can be configured to transmit dataaccording to a fourth maximum throughput. The third maximum throughputcan be greater than the fourth maximum throughput. The method canfurther include transmitting, by the second network switch using thefourth transceiver according to the fourth maximum throughput, seconddata to each of the first network switches. The second data can includea plurality of second optical subcarriers. Each second opticalsubcarrier can be associated with a different one of the first networkswitches. The method can further include receiving, by the each of thefirst network switches using a respective one of the fourthtransceivers, the second data from the second network switch, andextracting, by the each of the first network switches from the seconddata, a respective portion of the second data addressed to the firstnetwork switch.

In some implementations, extracting the respective portion of the seconddata corresponding to the first network switch can include extracting aportion of the second data from the second optical subcarrier associatedwith the first network switch.

In some implementations, the second network switch can further includeone or more fifth transceivers. The method can further includetransmitting, receiving or both transmitting and receiving, by thesecond network switch, third data from a wide area network using the oneor more fifth transceivers.

In some implementations, at least one of the first network switches canbe a top of rack network switch.

In some implementations, the second network switch can be a core networkswitch.

In some implementations, the method can further include transmitting, byat least one of the first server computers using the second transceiver,second data to the first network switch according to the second maximumthroughput. The second data can include a second optical subcarrier. Thesecond optical subcarrier can be associated with the first networkswitch.

In some implementations, the first data can be transmitted using thefirst transceiver of the first network switch to each of the secondreceivers of the first server computers.

In some implementations, the second data can be transmitted using thesecond transceiver of the at least one of the first server computers tothe first transceiver of the first network switch.

In another aspect, a system includes a plurality of network nodes. Eachnetwork node includes one or more respective first transceivers. Eachfirst transceiver is configured to transmit data according to a firstmaximum throughput. Each network node also includes one or morerespective second transceivers. Each second transceiver is configured totransmit data according to a second maximum throughput. The firstmaximum throughput is greater than the second maximum throughput. Afirst network node from among the plurality of network nodes isconfigured to transmit, using a respective one of the firsttransceivers, first data to two or more second network nodes from amongthe plurality of network nodes according to the first maximumthroughput. The first data includes a plurality of optical subcarriers.Each optical subcarrier is associated with a different one of the twomore other network nodes. The two or more second network nodes areconfigured to receive, using respective ones of the second transceivers,the first data from the first network node.

Implementations of this aspect can include one or more of the followingfeatures.

In some implementations, each network node of the plurality of networknodes can be communicatively coupled to each other network node of theplurality of network nodes.

In some implementations, for each network node of the plurality ofnetwork nodes, at least one of the first transceivers of the networknode can be communicatively coupled to at least one of the secondtransceivers of each other network node of the plurality of networknodes.

In some implementations, at least one of the network nodes of theplurality of network nodes can be communicatively coupled to only asubset the other network nodes of the plurality of network nodes.

In some implementations, for each network node of the plurality ofnetwork nodes, at least one of the first transceivers of the networknode can be communicatively coupled to at least one of the secondtransceivers of only a subset of the other network nodes of theplurality of network nodes.

In some implementations, each of the two more second network nodes canbe configured to extract, from the first data, a portion of the firstdata addressed to the that second network node.

In some implementations, each of the two more other second network nodescan be configured to extract the portion of the first data correspondingto the network node by extracting the portion of the first data from theoptical subcarrier associated with that second network node.

In some implementations, at least some of the first transceivers of thefirst network node can be communicatively coupled to at least two of thesecond transceivers of the second network node.

In some implementations, first data can be transmitted using the firsttransceiver of the first network node to each of the second receivers ofthe two or more second network nodes.

In some implementations, at least one of the two or more second networknodes can be configured to transmit, using the second transceiver,second data to the first network node according to the second maximumthroughput. The second data can include a second optical subcarrier. Thesecond optical subcarrier can be associated with the first network node.

In another aspect, a method includes interconnecting a plurality ofnetwork nodes. Each network node includes one or more respective firsttransceivers. Each first transceiver is configured to transmit dataaccording to a first maximum throughput. Each network node also includesone or more respective second transceivers. Each second transceiver isconfigured to transmit data according to a second maximum throughput.The first maximum throughput is greater than the second maximumthroughput. The method also includes transmitting, by a first networknode from among the plurality of network nodes using a respective one ofthe first transceivers, first data to two or more second network nodesfrom among the plurality of network nodes according to the first maximumthroughput. The first data includes a plurality of optical subcarriers.Each optical subcarrier is associated with a different one of the twomore other network nodes. The method also includes receiving, by the twoor more second network nodes using respective ones of the secondtransceivers, the first data from the first network node.

Implementations of this aspect can include one or more of the followingfeatures.

In some implementations, each network node of the plurality of networknodes can be communicatively coupled to each other network node of theplurality of network nodes.

In some implementations, for each network node of the plurality ofnetwork nodes, at least one of the first transceivers of the networknode can be communicatively coupled to at least one of the secondtransceivers of each other network node of the plurality of networknodes.

In some implementations, at least one of the network nodes of theplurality of network nodes can be communicatively coupled to only asubset the other network nodes of the plurality of network nodes.

In some implementations, for each network node of the plurality ofnetwork nodes, at least one of the first transceivers of the networknode ca be communicatively coupled to at least one of the secondtransceivers of only a subset of the other network nodes of theplurality of network nodes.

In some implementations, the method can further include extracting, byeach of the two more second network nodes, from the first data, aportion of the first data addressed to the that second network node.

In some implementations, extracting, by each of the two more secondnetwork nodes, the portion of the first data corresponding to thenetwork node can include extracting the portion of the first data fromthe optical subcarrier associated with that second network node.

In some implementations, at least some of the first transceivers of thefirst network node can be communicatively coupled to at least two of thesecond transceivers of the second network node.

In some implementations, the first data can be transmitted using thefirst transceiver of the first network node to each of the secondreceivers of the two or more second network nodes.

In some implementations, the method can further include transmitting,using the second transceiver, second data to the first network nodeaccording to the second maximum throughput. The second data can includea second optical subcarrier. The second optical subcarrier can beassociated with the first network node.

In another aspect, a method includes monitoring network traffictransmitted between a plurality of network nodes via a communicationsnetwork, ranking subsets of the network traffic according to one or moreranking criteria, and deploying a mesh network between the plurality ofnetwork nodes based on the ranking of the subsets of the networktraffic. The mesh network includes a plurality of network links. Eachnetwork link communicatively couples a respective network node fromamong the plurality of network nodes to another respective network nodefrom among the plurality of network nodes.

Implementations of this aspect can include or more of the followingfeatures.

In some implementations, the one or more ranking criteria can include acriterion regarding a data size of the network traffic transmittedbetween respective network nodes from among the plurality of networknodes.

In some implementations, the one or more ranking criteria can include acriterion regarding a frequency by which the network traffic istransmitted between respective network nodes from among the plurality ofnetwork nodes.

In some implementations, the one or more ranking criteria can include acriterion regarding a directionality by which the network traffic istransmitted between respective network nodes from among the plurality ofnetwork nodes.

In some implementations, the one or more ranking criteria can include acriterion regarding a utilization percentage of the communicationsnetwork in transmitting the network traffic.

In some implementations, deploying the mesh network between theplurality of network nodes can include determining, a respective rankfor each of the subsets of the network traffic. Each of the subsets ofthe network traffic can be transmitted from a respective source networknode from among the plurality of network nodes to a respectivedestination network node from among the plurality of network nodes.Deploying the mesh network between the plurality of network nodes canalso include determining that a first subset of the network traffic hasthe highest rank from among the subsets of the network traffic, anddeploying a network link between the source network node and thedestination node corresponding to the first subset of the networktraffic.

In some implementations, deploying the mesh network between theplurality of network nodes can include determining that a second subsetof the network traffic has the second highest rank from among thesubsets of the network traffic, and deploying a network link between thesource network node and the destination node corresponding to the secondsubset of the network traffic.

In some implementations, the method can include transmitting one or moreoptical subcarriers using the plurality of network links.

In some implementations, at least one of the network links cancommunicatively couple (i) a first transceiver of a first network nodefrom among the plurality of network nodes and (ii) a second transceiverof a second network node from among the plurality of network nodes. Thefirst transceiver can be configured to transmit data using the at leastone of the network links according to a first maximum throughput. Thesecond transceiver can be configured to transmit data according to asecond maximum throughput. The first maximum throughput can be greaterthan the second maximum throughput.

In some implementations, the mesh network can communicatively couple atleast one network node from among the plurality of network nodes to onlya subset of other network nodes from among the plurality of networknodes.

In some implementations, the method can include removing at least aportion of the communications network after deploying the mesh network.

In some implementations, deploying the mesh network can includedeploying network links between the plurality of network nodes until oneor more stop criteria are met.

In some implementations, the one or more stop criteria can include acriterion that a number of deployed network links equals to maximumnumber of network links.

In some implementations, the one or more stop criteria can include acriterion that the subsets of the network traffic associated with thedeployed network links account for a threshold percentage of the networktraffic.

In some implementations, the one or more stop criteria can include acriterion that an amount of monetary resources allotted or used todeploy the network links meets or exceeds a threshold amount.

In another aspect, a non-transitory, computer-readable storage mediumhas instructions stored thereon, that when executed by one or moreprocessors, cause the one or more processors to perform certainoperations. The operations includes monitoring network traffictransmitted between a plurality of network nodes via a communicationsnetwork, ranking subsets of the network traffic according to one or moreranking criteria, and determining a deployment of a mesh network betweenthe plurality of network nodes based on the ranking of the subsets ofthe network traffic. The mesh network includes a plurality of networklinks. Each network link communicatively couples a respective networknode from among the plurality of network nodes to another respectivenetwork node from among the plurality of network nodes.

Implementations of this aspect can include one or more of the followingfeatures.

In some implementations, determining the deployment the mesh networkbetween the plurality of network nodes can include determining, arespective rank for each of the subsets of the network traffic. Each ofthe subsets of the network traffic can be transmitted from a respectivesource network node from among the plurality of network nodes to arespective destination network node from among the plurality of networknodes. Determining the deployment the mesh network between the pluralityof network nodes can also include determining that a first subset of thenetwork traffic has the highest rank from among the subsets of thenetwork traffic, and determining that a network link be deployed betweenthe source network node and the destination node corresponding to thefirst subset of the network traffic.

In some implementations, determining the deployment the mesh networkbetween the plurality of network nodes can include determining that asecond subset of the network traffic has the second highest rank fromamong the subsets of the network traffic, and determining that a networklink be deployed between the source network node and the destinationnode corresponding to the second subset of the network traffic.

In some implementations, the operations can further include transmittingone or more optical subcarriers using the plurality of network links.

In another aspect, a system includes one or more processors, and memorystoring instructions that when executed by the one or more processors,cause the one or more processors to perform certain operations. Theoperations include monitoring network traffic transmitted between aplurality of network nodes via a communications network, ranking subsetsof the network traffic according to one or more ranking criteria, anddetermining a deployment of a mesh network between the plurality ofnetwork nodes based on the ranking of the subsets of the networktraffic. The mesh network includes a plurality of network links. Eachnetwork link communicatively couples a respective network node fromamong the plurality of network nodes to another respective network nodefrom among the plurality of network nodes.

In another aspect, a system includes a first network node, a secondnetwork node communicatively coupled to the first network node, and athird network node communicatively coupled to the second network node.The first network node is configured to generate a first opticalsubcarrier representing first data, and transmit the first opticalsubcarrier to the second network node. The second network node isconfigured to receive the first optical subcarrier from the firstnetwork node, generate a second optical subcarrier representing thefirst data, wherein the second optical subcarrier is different from thefirst optical subcarrier, and transmit the second optical subcarrier tothe third network node.

Implementations of this aspect can include one or more of the followingfeatures.

In some implementations, the third network node can be configured toreceive the second optical subcarrier from the second network node, anddetermine the first data based on the second optical subcarrier.

In some implementations, the system can further include a fourth networknode communicatively coupled to the second network node. The secondnetwork node can be configured to generate a third optical subcarrierrepresenting the first data, where the third optical subcarrier isdifferent from the second optical subcarrier, and transmit the thirdoptical subcarrier to the fourth network node. The fourth network nodecan be configured to receive the third optical subcarrier from thesecond network node, and determine the first data based on the thirdoptical subcarrier.

In some implementations, the system can further include a fourth networknode communicatively coupled to the third network node. The thirdnetwork node can be configured to receive the second optical subcarrierfrom the second network node, generate a third optical subcarrierrepresenting the first data, where the third optical subcarrier isdifferent from the second optical subcarrier, and transmit the thirdoptical subcarrier to the fourth network node. The fourth network nodecan be configured to receive the third optical subcarrier from the thirdnetwork node, and determine the first data based on the third opticalsubcarrier.

In some implementations, the system can further include a fourth networknode communicatively coupled to the second network node. The thirdnetwork node can be associated with the second optical subcarrier. Thefourth network node can be associated with a third optical subcarrier,where the third optical subcarrier is different from the second opticalsubcarrier. The second network node can be configured to transmit thesecond optical subcarrier to the third network node and the fourthnetwork node concurrently.

In some implementations, the second network node can be configured togenerate a third optical subcarrier representing second data, andtransmit the third optical subcarrier to the third network node and thefourth network node concurrently.

In some implementations, the second network node can be configured totransmit the second optical subcarrier and the third optical subcarrierconcurrently to each of the third network node and the fourth networknode.

In some implementations, the second network node can be configured totransmit the second optical subcarrier to the third network node and thefourth network node at a first time, and transmit the third opticalsubcarrier to the third network node and the fourth network node at asecond time different from the first time.

In some implementations, the first network node can include a firstlaser configured to generate the first optical subcarrier by modulatingan output of the first laser according to a first carrier frequency.

In some implementations, the second network node can include a secondlaser configured to generate the second optical subcarrier by modulatingan output of the second laser according to a second carrier frequency.

In some implementations, the first optical subcarrier and the secondoptical subcarrier can be Nyquist subcarriers.

In some implementations, the second network node can be configuredinterpret the first optical subcarrier according to a local oscillatorsignal having a first frequency, and generate the second opticalsubcarrier according to a transmitter oscillator signal having a secondfrequency. The first frequency can be equal to the second frequency.

In some implementations, the local oscillator signal and the transmitteroscillator signal can be provided by a common laser.

In another aspect, a method includes generating, by a first networknode, a first optical subcarrier representing first data; transmitting,by the first network node, the first optical subcarrier to the secondnetwork node; receiving, by the second network node, the first opticalsubcarrier from the first network node; generating, by the secondnetwork node, a second optical subcarrier representing the first data,where the second optical subcarrier is different from the first opticalsubcarrier; and transmitting, by the second network node, the secondoptical subcarrier to a third network node.

Implementations of this aspect can include one or more of the followingfeatures.

In some implementations, the method can include receiving, by the thirdnetwork node, the second optical subcarrier from the second networknode, and determining, by the third network node, the first data basedon the second optical subcarrier.

In some implementations, the method can include generating, by thesecond network node, a third optical subcarrier representing the firstdata. The third wavelength can be different from the second opticalsubcarrier. The method can also include transmitting, by second networknode, the third optical subcarrier to a fourth network node; receiving,by the fourth network node, the third optical subcarrier from the secondnetwork node; and determining, by fourth network node, the first databased on the third optical subcarrier.

In some implementations, the method can include receiving, by thirdnetwork node, the second optical subcarrier from the second networknode; generating, by third network node, a third optical subcarrierrepresenting the first data, where the third optical subcarrier isdifferent from the second optical subcarrier; transmitting, by the thirdnetwork node, the third optical subcarrier to a fourth network node;receiving, by the fourth network node, the third optical subcarrier fromthe third network node; and determining, by the fourth network node, thefirst data based on the third signal.

In some implementations, the third network node can be associated withthe second optical subcarrier. A fourth network node can be associatedwith a third optical subcarrier. The third optical subcarrier can bedifferent from the second optical subcarrier. The method can furtherinclude transmitting, by the second network node, the second opticalsubcarrier to the third network node and the fourth network nodeconcurrently. \

In some implementations, the method can include generating, by thesecond network node, a third optical subcarrier representing seconddata, and transmitting, by the second network node, the third opticalsubcarrier to the third network node and the fourth network nodeconcurrently.

In some implementations, the method can include transmitting, by thesecond network node, the second optical subcarrier and the third opticalsubcarrier concurrently to each of the third network node and the fourthnetwork node.

In some implementations, the second optical subcarrier can betransmitted to the third network node and the fourth network node at afirst time. The third optical subcarrier can be transmitted to the thirdnetwork node and the fourth network node at a second time different fromthe first time.

In some implementations, the method can include generating, by a firstlaser of the first network node, the first optical subcarrier bymodulating an output of the first laser according to a first carrierfrequency.

In some implementations, the method can include generating, by a secondlaser of the second network node, the second optical subcarrier bymodulating an output of the second laser according to a second carrierfrequency.

In some implementations, the first optical subcarrier and the secondoptical subcarrier can be Nyquist subcarriers.

In some implementations, the method can further include interpreting, bythe second network node, the first optical subcarrier according to alocal oscillator signal having a first frequency. The second opticalsubcarrier can be generated according to a transmitter oscillator signalhaving a second frequency. The first frequency can be equal to thesecond frequency.

In some implementations, the local oscillator signal and the transmitteroscillator signal can be provided by a common laser.

In another aspect, a node includes a first transceiver, and a secondtransceiver. The node is configured to receive, using the firsttransceiver, a first optical subcarrier representing first data from asecond node communicatively coupled the node, and transmit, using thesecond transceiver, a second optical subcarrier representing the firstdata to a third node communicatively coupled to the node. The secondoptical subcarrier is different from the first optical subcarrier.

In another aspect, a node includes a receiver, a switch circuit, and atransmitter. The receiver has a plurality of receiver outputs. Thereceiver is configured to receive a first modulated optical signalincluding a first plurality of optical subcarriers, and supply aplurality of data streams based on the first plurality of opticalsubcarriers. Each of the plurality of data streams is associated with acorresponding one of the plurality of optical subcarriers and issupplied from a respective one of the plurality of receiver outputs. Theswitch circuit has a plurality of switch inputs and a plurality ofswitch outputs. Each of the plurality of switch inputs is configured toreceive a respective one of the plurality of data streams. Each of theplurality of switch outputs is configured to supply a respective one ofthe plurality of data streams. The transmitter has a plurality ofinputs. Each of the inputs is coupled to a corresponding one of theplurality of switch outputs and is configured to receive a correspondingone of the plurality of data streams. The transmitter is configured tosupply a second modulated optical signal based on the plurality of datastreams. The second modulated optical signal carries a second pluralityof optical subcarriers. Each of the second plurality of opticalsubcarriers is associated with a corresponding one of the plurality ofdata streams.

Implementations of this aspect can include one or more of the followingfeatures.

In some implementations, one of the first plurality of opticalsubcarriers can have a first frequency and can be associated with one ofthe plurality of data streams. One of the second plurality of opticalsubcarriers can have a second frequency and can be associated with saidone of the plurality of data streams.

In some implementations, said one of the first plurality of opticalsubcarriers can carry information indicative of said one of theplurality of data streams. Said one of the second plurality of opticalsubcarriers can carry the information indicative of said one of theplurality of data streams.

In some implementations, the switch circuit can include a cross-pointswitch.

In some implementations, the receiver can include an optical hybridcircuit configured to receive at least a portion of the first modulatedoptical signal and a local oscillator signal. The receive can alsoinclude a photodiode circuit configured to receive mixing productsoutput from the optical hybrid circuit based on said at least theportion of the first modulated optical signal and the local oscillatorsignals, and supply first electrical signals based on the mixingproducts. The receive can also include analog-to-digital conversioncircuitry configured to receive the first electrical signals and supplysecond electrical signals based on the first electrical signals, thesecond electrical signals being digital signals. The receive can alsoinclude a digital signal processor configured to output the plurality ofdata streams based on the second electrical signals.

In some implementations, the node can include a local oscillator laserconfigured to supply the local oscillator signal.

In some implementations, the transmitter can include a digital signalprocessor configured to receive the plurality of data streams and outputa plurality of digital signals based on the plurality of data streams,digital-to-analog conversion circuitry configured to output analogsignals based on the digital signals, a plurality of driver circuitsconfigured to supply drive signals based on the analog signals, a laserconfigured to supply an optical signal, and a modulator configured toreceive the optical signal and supply the second modulated opticalsignal based on the drive signals.

In some implementations, each of the first plurality of opticalsubcarriers can be a Nyquist subcarrier.

In some implementations, each of the second plurality of opticalsubcarriers can be a Nyquist subcarrier.

In some implementations, during a first time interval, the switch canhave a first switch configuration, such that during a first timeinterval, a first one of the second plurality of optical subcarriershaving a first frequency carries information associated with one of theplurality of data streams. Further, during a second time interval, theswitch can have a second switch configuration, such that a second one ofthe second plurality of subcarriers carries the information.

In some implementations, the switch can have the first switchconfiguration based on a first control signal supplied to the switch andthe switch can have a second control signal based on a second controlsignal supplied to the switch.

In another aspect, a node includes a first digital signal processor, aswitch circuit, and second digital signal processor. The first digitalsignal processor is configured to supply a plurality of data streams,each of which is associated with a corresponding one of a firstplurality of optical subcarriers. The switch circuit has a plurality ofswitch inputs and a plurality of switch outputs. Each of the pluralityof switch inputs is configured to receive a respective one of theplurality of data streams, and supply a respective one of the pluralityof data streams. The second digital signal processor has a plurality ofDSP inputs. Each of the DSP inputs is configured to receive acorresponding one of the plurality of data streams from a respective oneof the plurality of switch outputs, such that, during a first timeinterval, and wherein one of the DSP inputs is configured to receive afirst one of the plurality of data streams and during a second timeinterval, different from the first time interval, said one of the DSPinputs is operable to receive a second one of the plurality of datastream.

Implementations of this aspect can include one or more of the followingfeatures.

In some implementations, the switch circuit can include a cross-pointswitch.

In some implementations, the node can include an optical hybrid circuitconfigured to receive at least a portion of a modulated optical signaland a local oscillator signal, the modulated optical signal includingthe plurality of optical subcarriers. The node can also include aphotodiode circuit configured to receive mixing products output from theoptical hybrid circuit based on said at least the portion of the firstmodulated optical signal and the local oscillator signal, the photodiodecircuit supplying first electrical signals based on the mixing products.The node can also include analog-to-digital conversion circuitryconfigured to receive the first electrical signals and supply secondelectrical signals based on the first electrical signals, the secondelectrical signals being digital signals. The first digital signalprocessor can be configured to supply the plurality of data streamsbased on the second electrical signals.

In some implementations, the node can include a local oscillator laserconfigured to supply the local oscillator signal.

In some implementations, the plurality of optical subcarriers can be afirst plurality of optical subcarriers. The node can further includedigital-to-analog conversion circuitry configured to output analogsignals based on the plurality of data streams, a plurality of drivercircuits configured to supply drive signals based on the analog signals,a laser that configured to supply an optical signal, and a modulatorconfigured to receive the optical signal and supply a modulated opticalsignal based on the drive signals, the modulated optical signalincluding a second plurality of optical subcarriers.

In some implementations, each of the plurality of optical subcarrierscan be a Nyquist subcarrier.

In some implementations, each of the first plurality of opticalsubcarriers and each of the second plurality of optical subcarriers canbe a Nyquist subcarrier.

In some implementations, one of the first plurality of subcarriers canbe associated with one of the plurality data streams during the firstinterval and one of the second plurality of optical subcarriers can beassociated with said one of the plurality of data streams.

In some implementations, said one of the first plurality of subcarrierscan have a first frequency and said one of the second plurality ofsubcarriers can have a second frequency different from the firstfrequency.

In some implementations, the second plurality of subcarriers can have afrequency that is different from each of the frequencies of the firstplurality of subcarriers.

The details of one or more embodiments are set forth in the accompanyingdrawings and the description below. Other features and advantages willbe apparent from the description and drawings, and from the claims.

DESCRIPTION OF DRAWINGS

FIGS. 1 and 2 are block diagrams showing examples of networks.

FIG. 3A is a block diagram showing an example of a primary node.

FIG. 3B is a block diagram showing an example of a secondary node.

FIG. 4 is an example of a spectral plot showing optical subcarriers.

FIG. 5 shows an example of a primary node transmitter.

FIG. 6A is a block diagram showing an example of a primary nodetransmitter digital signal processor (DSP).

FIG. 6B illustrates a portion of a primary node transmitter DSP ingreater detail.

FIG. 6C illustrates a portion of a primary node transmitter DSP ingreater detail.

FIG. 7A shows an example of a secondary node receiver.

FIG. 7B shows an example of a bandwidth of a secondary node.

FIG. 7C shows a control circuit.

FIG. 8 shows an example of a secondary node receiver DSP.

FIGS. 9A and 9B show example interconnections between a primary node andmultiple secondary nodes.

FIG. 10A-10D show example interconnections between multiple nodes.

FIG. 11 shows an example system for routing data in a datacenter.

FIG. 12A shows interconnections between a top of rack (ToR) switch andmultiple server computers in the system shown in FIG. 11.

FIG. 12B shows example interconnections between a core switch andmultiple ToR switches in the system shown in FIG. 11.

FIGS. 13-15 show example systems having a mesh topology.

FIGS. 16A-16F show an example process for deploying a mesh network.

FIG. 17A shows an example system for performing frequency or wavelengthtranslation.

FIG. 17B shows another example system for performing frequency orwavelength translation.

FIG. 18A is a flow diagram of an example process for transmitting data.

FIG. 18B is a flow diagram of another example process for transmittingdata.

FIG. 18C is a flow diagram of an example process for designing anddeploying a network having an asymmetric mesh configuration

FIG. 18D is a flow diagram of another example process for transmittingdata.

FIG. 19 is a diagram of an example computer system.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

In an example communications network, a first node of the network cantransmit data to multiple second nodes of the network concurrently, suchthat similar data is “multicast” to multiple nodes at the same time.Upon receipt of the data, each of the second nodes can selectivelyretain one or more portions of the data (e.g., the portions of the datathat are intended for the node) and discard one or more other portionsof the data (e.g., the portions of the data that are intended for othernodes). In some implementations, data can be transmitted as one or moreoptical carriers.

Further, at least some of the second nodes can include components thathave different (e.g., lower) capabilities than the components includedin first node. For example, the bandwidth or the data capacity of atleast some of the second nodes can be less than that associated with thefirst node, such that the capacity associated with each of those secondnodes is less than that of the first node. Accordingly, the first nodecan transmit data to each of those secondary nodes according to a higherbit rate (e.g., using a higher capacity transceiver), and each of thosesecond nodes can transmit data to the first node according to a lowerbit rate (e.g., using a lower capacity transceiver). Accordingly,downstream data (e.g., from the first node to the second nodes) istransmitted according to a larger pooled allocation of bandwidth,whereas upstream data (e.g., from each of the second nodes to the firstnode) is transmitted according to respective smaller dedicatedallocations of bandwidth.

Example implementations of the aforementioned aspects are described infurther detail herein.

Further, the implementations described herein can provide can provideone or more technical benefits in the context of computer networking.For example, in at least some implementations, this configurationenables traffic to be transmitted in certain directions according to apooled allocation of bandwidth (e.g., shared among multiple nodes of thenetwork to alleviate congestion), while also enabling traffic to betransmitted in certain other directions according to smaller dedicatedallocations of bandwidth. Further, in at least some implementations,this configuration enables a network to be deployed and maintained in amore cost efficient manner (e.g., compared to using solely high capacitytransceivers across the entirety of the network).

FIG. 1 illustrates an example aggregation network 100 in which a primarynode 110 communicates with multiple secondary nodes 112-j to 112-m(which sometimes may be referred to individually or collectively assecondary node(s) 112). In some implementations, one or more of thesecondary nodes 112 can be remote from the primary node 110.

The primary node 110 transmits data in the form of one or more opticalsubcarriers (e.g., as described in greater detail below) in a downstreamdirection to a splitter 114 via an optical communication path 111. Thesplitter 114 receives the optical subcarriers, and provides apower-split portion of each optical subcarrier to a corresponding one ofthe secondary nodes 112-j to 112-m via a respective one of the opticalcommunication paths 113-j to 113-m. Each of the optical communicationpaths 111 and 113-j to 113-m can include or more segments of opticalfiber, optical amplifiers, reconfigurable add-drop multiplexers(ROADMs), and/or other optical fiber communication equipment.

The primary node 110 has a data capacity to receive n Gbit/s of data(e.g., a data stream) for transmission to the secondary nodes 112. Eachsecondary node 112 may receive and output a portion of the data that isinput into primary node 110 (e.g., to a user or customer). In thisexample, the secondary nodes 112-j, 112-k, 112-1, and 112-m areconfigured to output j Gbit/s, k Gbit/s, l Gbit/s, and m Gbit/s of data(e.g., data streams), respectively, where the sum of the j, k, l, and mare equal n (where j, k, l, m, and n are positive numbers).

FIG. 2 shows the transmission of additional optical subcarriers in anupstream direction from the secondary nodes 112-j to 112-m to theprimary node 110. In some implementations, each of the secondary nodes112-j to 112-m can transmit a corresponding group of optical subcarriersor one optical subcarrier to an optical combiner 116 via a respectiveone of optical communication paths 115-1 to 115-m. The optical combiner116 can, in turn, combine the received optical subcarriers from thesecondary nodes 112-j to 112-m onto the optical communication path 117.In some implementations, the optical communication paths 115-1 to 115-mand 117 can have a similar construction as that of the opticalcommunication paths 111 and 112-1 to 112-m.

As further shown in FIG. 2, each of the secondary nodes 112-j to 112-mreceives a respective data stream having a corresponding data rate of jGbit/s, k Gbit/s, l Gbit/s, and m Gbit/s. At the primary node 110, datacontained in these streams can be output such that the aggregate datasupplied by the primary node 110 is n Gbit/s (e.g., such that n equalsthe sum of j, k, l, and m).

In some implementations, optical subcarriers can be transmitted in bothan upstream and downstream direction over the same optical communicationpath. For instance, selected optical subcarriers can be transmitted inthe downstream direction from the primary node 110 to the secondarynodes 112, and other optical subcarriers can be transmitted in theupstream direction from the secondary nodes 112 to the primary node 110.

In some implementations, the network 100 can include additional primaryand/or secondary nodes and optical communication paths, or fewer primaryand/or secondary nodes and optical communication paths. In someimplementations, the network 100 can have a configuration different fromthat described above. For example, network 100 can have a meshconfiguration or a point-to-point configuration.

FIG. 3 illustrates an example primary node 110 in greater detail. Inthis example, the primary node 110 includes a transmitter 202 thatsupplies a downstream modulated optical signal including opticalsubcarriers, and a receiver 204 that receives upstream opticalsubcarriers carrying data originating from one or more of the secondarynodes 112.

FIG. 3 illustrates an example secondary node 112 in greater detail. Inthis example, the secondary node 112 includes a receiver circuit 302that receives one or more downstream transmitted optical subcarriers,and a transmitter circuit 304 that transmits one or more opticalsubcarriers in the upstream direction.

FIG. 4 illustrates an example of a transmission spectrum that canaccommodate twenty optical subcarriers SC0 to SC19 that can be outputfrom primary node transmitter 202. Each of the optical subcarriers SC0to SC19 has a corresponding one of frequencies f0 to f19. In someimplementations, the optical subcarriers SC0 to SC19 are Nyquistsubcarriers. Nyquist subcarriers are a group of optical signals, eachcarrying data, where (i) the spectrum of each such optical signal withinthe group is sufficiently non-overlapping such that the optical signalsremain distinguishable from each other in the frequency domain, and (ii)such group of optical signals is generated by modulation of light from asingle laser. In general, each subcarrier can have an optical spectralbandwidth that is at least equal to the Nyquist frequency, as determinedby the baud rate of such subcarrier.

In some implementations, each of the secondary nodes 112 can includecomponents that have different (e.g., lower) capabilities than thecomponents included in primary node 110. For example, the bandwidth orthe data capacity of the secondary nodes 112 can be less than thatassociated with the primary node 110, such that the capacity associatedwith each of the secondary nodes 112 is less than that of the primarynode 110.

Further, as shown in FIG. 4, the primary node 110 can have a bandwidthBW-P, such that the data carried by each of the optical subcarriers SC1to SC20 can be processed, recovered, and output either from thetransmitter 202 or received from the receiver 204. In contrast, each ofthe secondary nodes 112-j to 112-m can have a respective one ofbandwidths BWj to BWm, such that each secondary node has a dataprocessing capacity or is capable of processing and outputting datacarried by multiple optical subcarriers (e.g., up to nine opticalsubcarriers, according to the example shown in FIG. 4).

In some implementations, certain components of the secondary nodes 112(e.g., optical components and certain electrical components) can beconfigured such that they are capable of processing signals only over alimited frequency range or bandwidth. The limited frequency range orbandwidth can be less than the range of signal frequencies that can beaccommodated by the optical and electrical components in the primarynode 110. For example, electrical components, such as digital-to-analog(DACs), analog-to-digital converters (ADCs), and digital signalprocessors (DSPs), and optical components, such as modulators, insecondary nodes 112 can have an associated bandwidth that is less thanthe corresponding components in the primary node 110. This can beuseful, for example, in reduce the cost of deploying and/or maintainingthe network.

Example bandwidths of each of the secondary nodes 112 are shown in FIG.4. In particular, a bandwidth BWj associated with the secondary node112-j extends over or encompasses a range including frequencies f0 to f8of the optical subcarriers SC0 to SC8, respectively; a bandwidth BWkassociated with the secondary node 112-k extends over or encompasses arange including frequencies f5 to f13 of the optical subcarriers SC5 toSC13, respectively; a bandwidth BW1 associated with the secondary node112-1 extends over or encompasses a range including frequencies f10 tof18 of the optical subcarriers SC10 to SC18, respectively; and abandwidth BWm associated with the secondary node 112-m extends over orencompasses a range including frequencies f11 to f19 of the opticalsubcarriers SC11 to SC19, respectively. In contrast, the bandwidth ofthe primary node 110, BW-P, encompasses the entire range of frequenciesf0-f19 of the optical subcarriers SC0 to SC19.

As also shown in FIG. 4, certain optical subcarriers can havefrequencies that fall within multiple bandwidths. For example, theoptical subcarriers SC5 and SC6 can have frequencies that fall within abandwidth BWj and a bandwidth BWk. Therefore, the data carried by suchoptical subcarriers can be detected and selectively output from eitherthe secondary node 112-j or the secondary node 112-k. For example, if acustomer requires that more data be received and output from thesecondary node 112-k and less data be output from the secondary node112-j, the secondary nodes 112-j and 112-k can be controlled ordynamically configured such that the data carried by the opticalsubcarriers SC5 and SC6 are assigned to and output from the secondarynode 112-k, but not the secondary node 112-j. Accordingly, the dataoutput from each secondary node may be adapted to customer requirementsthat vary over time.

As also shown in FIG. 4, certain option subcarriers, such as the opticalsubcarriers SC2, SC7, SC12, and SC17, can be designated or dedicated tocarry information related to a parameter or characteristic associatedwith one or more of the secondary nodes 112. For example, suchparameters can correspond to an amount of data, data rate, or capacityto be output by one or more secondary nodes. In particular, such opticalsubcarriers ca carry information, for example, to configure or adjustthe amount of data, capacity or data rate of data output from thesecondary nodes 112-j to 112-m, respectively. As another example, eachof these optical subcarriers can carry user or customer data (alsoreferred to as client data) in addition to control information. In theexample shown in FIG. 4, only the optical subcarriers SC2, SC7, SC12,and S17 are transmitted.

As another example, the subcarriers SC2, SC7, SC12, and SC17 can bemodulated to carry control or operations, administration, andmaintenance (OAM) information and related data corresponding toparameters associated therewith, such as the capacity and status of thesecondary nodes 112. As another example, the subcarrier SC2 can bemodulated carry such control and parameter information associated withthe secondary node 112-j, the subcarrier SC7 can modulated to carry suchcontrol and parameter information associated with the secondary node112-k, the subcarrier SC12 can be modulated to carry such control andparameter information associated with the secondary node 112-1, and thesubcarrier SC17 can be modulated to carry such control and parameterinformation associated with the secondary node 112-m. As anotherexample, optical subcarriers can be modulated to carry informationrelated to a parameter associated the timing and scheduling of datatransmission from the secondary nodes 112 to primary the node 110.

Data allocation and subcarrier transmission are described next withreference to FIG. 5 and FIGS. 6A-6C.

FIG. 5 illustrates the transmitter 202 of the primary node 110 ingreater detail. The transmitter 202 includes a plurality of circuits orswitches SW, as well as a transmitter DSP (TX DSP) 502 and a D/A andoptics block 501. In this example, twenty switches (SW-0 to SW-19) areshown, although more or fewer switches can be provided than that shownin FIG. 5. In some implementations, each switch can have two respectiveinputs: the first input can receive user data, and the second input canreceive control information or signals (CNT). Each of the switches SW-0to SW-19 can receive a respective one of the control signals SWC-0 toSWC-19 output from the control circuit 571 (which can include one ormore microprocessors, field programmable gate arrays (FPGA), or otherprocessor circuits). Based on the received control signal, each of theswitches SW-0 to SW19 selectively outputs any one of the data streamsD-0 to D-19, or a control signal CNT-0 to CNT-19. The control signalsCNT can be any combination of configuration bits for control and/ormonitoring purposes. For example, the control signals CNT can includeinstructions to one or more of the secondary nodes 112 to change thedata output from the secondary nodes 112, such as by identifying theoptical subcarriers associated with such data. As another example, thecontrol signals can include a series of known bits used in the secondarynodes 112 to “train” the receiver to detect and process such bits sothat the receiver can further process subsequent bits. As anotherexample, the control channel CNT can include information that may beused by the polarization mode dispersion (PMD) equalizer circuits 825,discussed below, to correct for errors resulting from polarizationrotations of the X and Y components of one or more of the opticalsubcarriers. In a further example, the control information CNT can usedto restore or correct phase differences between a laser transmit-sidelaser 508 and a local oscillator laser 710 in each of the secondarynodes 112. Such detected phase differences may be referred to as cycleslips. In a further example, the control information CNT can be used torecover, synchronize, or correct timing differences between clocksprovided in the primary node 110 and the secondary node 112.

In some implementations, one or more of the switches SW can be omitted,and the control signals CNT can be supplied directly to the DSP 502.Moreover, each input to the DSP 502, such as the inputs to FEC encoders602 described below (see FIG. 6A), can receive a combination of controlinformation (e.g., as described above) as well as user data.

In some implementations, the control signal CNT can include informationrelated to the number of optical subcarriers that are output from eachof the secondary nodes 112. Such selective transmission of opticalsubcarriers is described with reference to FIGS. 6A-6C. Although suchdescription is provided in connection with the primary node DSP 502,similar circuitry can be included in a DSP of the secondary node 112 toadjust or control the number of optical subcarriers output therefrom.

Based on the outputs of the switches SW-0 to SW-19, the DSP 502 cansupply a plurality of outputs to the D/A and optics block 501 includingdigital-to-analog conversion (DAC) circuits 504-1 to 504-4, whichconvert digital signal received from the DSP 502 into correspondinganalog signals. The D/A and optics block 501 also includes drivercircuits 506-1 to 506-2 that receive the analog signals from the DACs504-1 to 504-4 and adjust the voltages or other characteristics thereofto provide drive signals to a corresponding one of the modulators 510-1to 510-4.

The D/A and optics block 501 further includes modulators 510-1 to 510-4(e.g., Mach-Zehnder modulators (MZM)) that modulates the phase and/oramplitude of the light output from the laser 508. As further shown inFIG. 5, light output from the laser 508, also included in the block 501,is split such that a first portion of the light is supplied to a firstMZM pairing, including the MZMs 510-1 and 510-2, and a second portion ofthe light is supplied to a second MZM pairing, including the MZMs 510-3and 510-4. The first portion of the light is split further into thirdand fourth portions, such that the third portion is modulated by the MZM510-1 to provide an in-phase (I) component of an X (or TE) polarizationcomponent of a modulated optical signal, and the fourth portion ismodulated by the MZM 510-2 and fed to a phase shifter 512-1 to shift thephase of such light by 90 degrees in order to provide a quadrature (Q)component of the X polarization component of the modulated opticalsignal. Similarly, the second portion of the light is further split intofifth and sixth portions, such that the fifth portion is modulated bythe MZM 910-3 to provide an I component of a Y (or TM) polarizationcomponent of the modulated optical signal, and the sixth portion ismodulated by the MZM 510-4 and fed to a phase shifter 512-2 to shift thephase of such light by 90 degrees to provide a Q component of the Ypolarization component of the modulated optical signal.

The optical outputs of the MZMs 510-1 and 510-2 are combined to providean X polarized optical signal including I and Q components and are fedto a polarization beam combiner (PBC) 514 provided in block 501. Inaddition, the outputs of the MZMs 510-3 and 510-4 are combined toprovide an optical signal that is fed to polarization rotator 513,further provided in block 501, that rotates the polarization of suchoptical signal to provide a modulated optical signal having a Y (or TM)polarization. The Y polarized modulated optical signal also is providedto the PBC 514, which combines the X and Y polarized modulated opticalsignals to provide a polarization multiplexed (“dual-pol”) modulatedoptical signal onto an optical fiber 516, for example, which may beincluded as a segment of optical fiber in optical communication path111.

The polarization multiplexed optical signal output from the D/A andoptics block 501 includes the optical subcarriers SC0-SC19 noted above,such that each optical subcarrier has X and Y polarization componentsand I and Q components. Moreover, each of the optical subcarriers SC0 toSC19 can be associated with or correspond to a respective one of theoutputs of the switches SW-0 to SW-19. In some implementations, theswitches SW2, SW7, SW12, and SW17 can supply control information carriedby a respective one of the control signals CNT-2, CNT-7, CNT-12, andCNT-17 to DSP 502. Based on such control signals, the DSP 502 canprovide outputs that result in the optical subcarriers SC2, SC7, SC12,and SC17 carrying data indicative of the control information carried bythe CNT-2, CNT-7, CNT-12, and CNT-17, respectively. In addition, theremaining optical subcarriers SC0, SC1, SC3 to SC6, SC8 to SC11, SC13 toSC16, and SC18 to SC20 can carry information indicative of a respectiveone of the data streams D-0, D-1, D-3-D-6, D-8 to D-11, D-13 to D-16,and D-18 to D-20 output from a corresponding one of the switches SW0,SW1, SW3 to SW-6, SW-8 to SW11, SW13 to SW16, and SW18 to SW20. In someimplementations, at least some of the switches (e.g., SW0 to SW19, asshown in FIG. 5) can be omitted, such that data stream are supplieddirectly to the Tx DSP 502.

FIG. 6A shows an example of the TX DSP 502 in greater detail. The TX DSP502 can include FEC encoders 602-0 to 602-19, each of which can receivea respective one of a plurality of the outputs from the switches SW0 toSW19. The FEC encoders 602-0 to 602-19 carry out forward errorcorrection coding on a corresponding one of the switch outputs, such as,by adding parity bits to the received data. The FEC encoders 602-0 to602-19 can also provide timing skew between the subcarriers to correctfor skew induced by link between the nodes 110 and 112-j to 112-mdescribed above. In addition, the FEC encoders 602-0 to 602-19 caninterleave the received data.

Each of the FEC encoders 602-0 to 602-19 provides an output to acorresponding one of a plurality of bits-to-symbol circuits, 604-0 to604-19 (collectively referred to herein as “604”). Each of thebits-to-symbol circuits 604 can map the encoded bits to symbols on acomplex plane. For example, the bits-to-symbol circuits 604 can map fourbits to a symbol in a dual-polarization QPSK constellation. Each of thebits-to-symbol circuits 604 provides first symbols, having the complexrepresentation XI+j*XQ, associated with a respective one of the switchoutputs, such as D-0, to a DSP portion 603. Data indicative of suchfirst symbols is carried by the X polarization component of eachsubcarrier SC0-SC19.

Each of the bits-to-symbol circuits 604 can also provide second symbolshaving the complex representation YI+j*YQ, also associated with acorresponding output of the switches SW0-SW19. Data indicative of suchsecond symbols, however, is carried by the Y polarization component ofeach of subcarriers SC-0 to SC-19.

In some implementations, such mapping, as carried by the circuit 604-0to 604-19, can define a particular modulation format for eachsubcarrier. That is, such circuit can define a mapping for all theoptical subcarrier that is indicative of a binary phase shift keying(BPSK) modulation format, a quadrature phase shift keying (QPSK)modulation format, or an m-quadrature amplitude modulation (QAM, where mis a positive integer, e.g., 4, 8, 16, or 64) format. In anotherexample, one or more of the optical subcarriers can have a modulationformat that is different from the modulation format of other opticalsubcarriers. That is, one of the optical subcarriers can have a QPSKmodulation format and another optical subcarrier can have a differentmodulation format, such as 8-QAM or 16-QAM. In another example, one ofthe optical subcarriers can have an 8-QAM modulation format and anotheroptical subcarrier can have a 16 QAM modulation format. Accordingly,although all the optical subcarriers can carry data at the same data andor baud rate, one or more of the optical subcarriers can carry data at adifferent data or baud rate than one or more of the other opticalsubcarriers. Moreover, modulation formats, baud rates and data rates canbe changed over time depending on capacity requirements. Adjusting suchparameters can be achieved, for example, by applying appropriate signalsto mappers 604 based on control information or data.

As further shown in FIG. 6A, each of the first symbols output from eachof the bits-to-symbol circuits 604 is supplied to a respective one ofthe first overlap and save buffers 605-0 to 605-19 (collectivelyreferred to herein as the overlap and save buffers 605). Each theoverlap and save buffers 605 can buffer a particular number of symbols(e.g., 256 symbols). In some implementations, each of the overlap andsave buffers 605 can receive 128 of the first symbols or another numberof such symbols at a time from a corresponding one of the bits to symbolcircuits 604. Thus, the overlap and save buffers 605 can combine 128 newsymbols from the bits to symbol circuits 605, with the previous 128symbols received from the bits to symbol circuits 605.

Each of the overlap and save buffers 605 supplies an output (e.g., inthe time domain) to a corresponding one of the fast Fourier transform(FFT) circuits 606-0 to 606-19 (collectively referred to as the “FFTs606”). In some implementations, the output can include 256 symbols oranother number of symbols. Each of the FFTs 606 converts the receivedsymbols to the frequency domain using or based on a fast Fouriertransform. Each of the FFTs 606 can provide the frequency domain data tothe bins and switches blocks 621-0 to 621-19. As discussed in greaterdetail below, the bins and switches blocks 621 include, can includememories or registers, also referred to as frequency bins (FB) orpoints, that store frequency components associated with each opticalsubcarrier.

Selected frequency bins FB are shown in FIG. 6B. Groups of suchfrequency bins FB are associated with give subcarriers. Accordingly, forexample, a first group of frequency bins, FB0-0 to FB0-n, is associatedwith SC0 and a second group of frequency bins FB19-0 to FB19-n with SC19(where n is a positive integer). As further shown in FIG. 10b , each ofthe frequency bins FB is further coupled to a respective one of switchesSW. For example, each of frequency bins FB0-0 to FB0-n is coupled to arespective one of switches SW0-0 to SW0-n, and each of FB19-0 to FB19-nis coupled to a respective one of switches or switch circuits SW19-0 toSW19-n.

Each of the switches SW selectively supplies either frequency domaindata output from one of the FFT circuits 606-0 to 606-19 or apredetermined value, such as 0. In order to block or eliminatetransmission of a particular subcarrier, the switches SW associated withthe group of frequency bins FB associated with that optical subcarrierare configured to supply the zero value to corresponding frequency bins.Accordingly, in order to block the optical subcarrier SC0, the switchesSW0-0′ to SW0-n′ supply zero (0) values to a respective one of thefrequency bins FB0-0 to FB0-n. Further processing of the zero (0) valuesby replicator components 1007, as well as other components and circuitsin the DSP 502, result in drive signals supplied to the modulators 510,such that the optical subcarrier SC0 is omitted from the optical outputfrom the modulators.

In contrast, the switches SW′ can be configured to supply the outputs ofthe FFTs 606 (e.g., frequency domain data FD) to corresponding frequencybins FB. Further processing of the contents of the frequency bins FB byreplicator components 607 and other circuits in DSP 502 result in drivesignals supplied to modulators 510, whereby, based on such drivesignals, optical subcarriers are generated that correspond to thefrequency bin groupings associated with that subcarrier.

In the example discussed above, the switches SW0-0′ to SW0-n′ supplyfrequency domain data FD0-0 to FD-n from the FFT 606-0 to a respectiveone of switches SW0-0 to SW0-n. These switches, in turn, supply thefrequency domain data to a respective one of the frequency bins FB0-0 toFB0-n for further processing, as described in greater detail below.

Each of replicator components or circuits 607-0 to 607-19 can replicatethe contents of the frequency bins FB and store such contents (e.g., forT/2 based filtering of the subcarrier) in a respective one of theplurality of replicator components. Such replication may increase thesample rate. In addition, the replicator components or circuits 607-0 to607-19 can arrange or align the contents of the frequency bins to fallwithin the bandwidths associated with the pulse shaped filter circuits608-0 to 608-19 described below.

Each of the pulse shape filter circuits 608-0 to 608-19 can apply apulse shaping filter to the data stored in the 512 frequency bins of arespective one of the plurality of replicator components or circuits607-0 to 607-19 to thereby provide a respective one of a plurality offiltered outputs, which are multiplexed and subject to an inverse FFT,as described below. The pulse shape filter circuits 608-1 to 608-19calculate the transitions between the symbols and the desired subcarrierspectrum so that the subcarriers can be packed together spectrally fortransmission (e.g., with a close frequency separation). The pulse shapefilter circuits 608-0 to 608-19 also can be used to introduce timingskew between the subcarriers to correct for timing skew induced by linksbetween nodes (e.g., the nodes shown in FIG. 1). The multiplexercomponent 609, which can include a multiplexer circuit or memory, canreceive the filtered outputs from the pulse shape filter circuits 608-0to 608-19, and multiplex or combine such outputs together to form anelement vector.

Next, the IFFT circuit or component 610-1 can receive the element vectorand provide a corresponding time domain signal or data based on aninverse fast Fourier transform (IFFT). In some implementations, the timedomain signal can have a rate of 64 GSample/s. The take last buffer ormemory circuit 611-1, for example, can select the last 1024 samples, oranother number of samples, from an output of the IFFT component orcircuit 610-1 and supply the samples to the DACs 504-1 and 504-2 (seeFIG. 5) at 64 GSample/s, for example. As noted above, the DAC 504-1 isassociated with the in-phase (I) component of the X pol signal, and theDAC 504-2 is associated with the quadrature (Q) component of the Y polsignal. Accordingly, consistent with the complex representation XI+jXQ,the DAC 504-1 receives values associated with XI and the DAC 504-2receives values associated with jXQ. As indicated by FIG. 5, based onthese inputs, the DACs 504-1 and 504-2 provide analog outputs to theMZMD 506-1 and the MZMD 506-2, respectively.

As further shown in FIG. 6A, each of the bits-to-symbol circuits 604-0to 604-19 outputs a corresponding one of symbols indicative of datacarried by the Y polarization component of the polarization multiplexedmodulated optical signal output on the fiber 516. As further notedabove, these symbols can have the complex representation YI+j*YQ. Eachsuch symbol can be processed by a respective one of the overlap and savebuffers 615-0 to 615-19, a respective one of the FFT circuits 616-0 to616-19, a respective one of the replicator components or circuits 617-0to 617-19, the pulse shape filter circuits 618-0 to 618-19, themultiplexer or memory 619, the IFFT 610-2, and the take last buffer ormemory circuit 611-2, to provide processed symbols having therepresentation YI+j*YQ in a manner similar to or the same as thatdiscussed above in generating processed symbols XI+j*XQ output from thetake last circuit 611-1. In addition, symbol components YI and YQ areprovided to the DACs 504-3 and 504-4 (FIG. 5), respectively. Based onthese inputs, the DACs 504-3 and 504-4 provide analog outputs to theMZMD 506-3 and the MZMD 506-4, respectively, as discussed above.

While FIG. 6A shows the DSP 502 as including a particular number andarrangement of functional components, in some implementations, the DSP502 can include additional functional components, fewer functionalcomponents, different functional components, or differently arrangedfunctional components. In addition, typically the number of overlap andsave buffers, FFTs, replicator circuits, and pulse shape filtersassociated with the X component can be equal to the number of switchoutputs, and the number of such circuits associated with the Y componentalso can be equal to the number of switch outputs. However, in otherexamples, the number of switch outputs can be different from the numberof these circuits.

As noted above, based on the outputs of the MZMDs 506-1 to 506-4, aplurality of the optical subcarriers SC0 to SC19 can be output onto theoptical fiber 516 (FIG. 5), which is coupled to the primary node 110.

In some implementations, the number of optical subcarriers transmittedfrom the primary node 110 to the secondary nodes 112 can vary over timebased, for example, on capacity requirements at the primary node and thesecondary nodes. For instance, if less downstream capacity is requiredinitially at one or more of the secondary nodes, the transmitter 202 inthe primary node 110 can be configured to output fewer opticalsubcarriers. In contrast, if further capacity is required later, thetransmitter 202 can provide more optical subcarriers.

In addition, if based on changing capacity requirements, a particularsecondary node 112 needs to be adjusted, the output capacity of suchsecondary node can be increased or decreased by increasing or decreasingthe number of optical subcarriers output from the secondary node.

As noted above, by storing and subsequently processing zeros (0s) orother predetermined values in the frequency bin FB groupings associatedwith a given optical subcarrier, that optical subcarrier can be removedor eliminated. To add or reinstate such an optical subcarrier, frequencydomain data output from the FFTs 606 can be stored in the frequency binsFB and subsequently processed to provide the corresponding opticalsubcarrier. Thus, optical subcarriers can be selectively added orremoved from the optical outputs of the primary node transmitter 202 andthe secondary node transmitter 304, such that the number of subcarriersoutput from such transmitters can be varied, as desired.

In the above example, zeros (0s) or other predetermined values arestored in selected frequency bins FBs to prevent transmission of aparticular optical subcarrier. In some implementations, such zeroes orvalues can instead be provided in a manner similar to that describedabove, at the outputs of corresponding replicator components 607 orstored in corresponding locations in the memory or multiplexer 609.Alternatively, the zeroes or values noted above can be provided in amanner similar to that described above, at corresponding outputs of thepulse shape filters 608.

In a further example, a corresponding one of the pulse shape filters608-1 to 608-19 can selectively generate zeroes or predetermined valuesthat, when further processed, also cause one or more of the opticalsubcarriers to be omitted from the output of either the primary nodetransmitter 202 or the secondary node transmitter 304. In particular, asshown in FIG. 6C, the pulse shape filters 608-0 to 608-19 are shown asincluding groups of multiplier circuits M0-0 to M0-n . . . M19-0 toM19-n (also individually or collectively referred to as M). Eachmultiplier circuit M constitutes part of a corresponding butterflyfilter. In addition, each multiplier circuit grouping is associated witha corresponding one of the optical subcarriers.

Each multiplier circuit M receives a corresponding one of outputgroupings RD0-0 to RD0-n RD19-0 to RD19-n from the replicator components607. In order to remove or eliminate one of optical subcarriers, themultiplier circuits M receiving the outputs within a particular groupingassociated with that optical subcarrier multiply such outputs by zero(0), such that each multiplier M within that group generates a productequal to zero (0). The zero products then are subject to furtherprocessing similar to that described above to provide drive signals tomodulators 510 that result in a corresponding optical subcarrier beingomitted from the output of the transmitter (e.g., either the transmitter202 or the transmitter 304).

In contrast, in order to provide an optical subcarrier, each of themultiplier circuits M within a particular groping can multiply acorresponding one of the replicator outputs RD by a respective one ofcoefficients C0-0 to C0-n . . . C19-0 to C19-n, which results in atleast some non-zero products being output. Based on the products outputfrom the corresponding multiplier grouping, drive signals are providedto the modulators 510 to output the desired optical subcarrier from thetransmitter (e.g., either the transmitter 202 or the transmitter 304).

Accordingly, in order to block or eliminate the optical subcarrier SC0,each of the multiplier circuits M0-0 to M0-n (associated with theoptical subcarrier SC0) can multiply a respective one of the replicatoroutputs RD0-0 to RD0-n by zero (0). Each such multiplier circuit,therefore, provides a product equal to zero, which is further processedsuch that resulting drive signals cause the modulators 510 to provide anoptical output without the optical subcarrier SC0. In order to reinstatethe optical subcarrier SC0, the multiplier circuits M0-0 to M0-nmultiply a corresponding one of the appropriate coefficients C0-0 toC0-n by a respective one of the replicator outputs RD0-0 to RD0-n toprovide products, at least some of which are non-zero. Based on theseproducts, the modulator drive signals are generated that result in theoptical subcarrier SC0 being output.

The above examples are described in connection with generating orremoving the X component of an optical subcarrier. The processes andcircuitry described above is employed or included in the DSP 502 andoptical circuitry used to generate the Y component of the subcarrier tobe blocked. For example, the switches and bins circuit blocks 622-0 to622-19, can have a similar structure and operate in a similar manner asthe switches and bins circuit blocks 621 described above to providezeroes or frequency domain data, as the case may be, to selectivelyblock the Y component of one or more the optical subcarriers.Alternatively, multiplier circuits, like those described above inconnection with FIG. 6C, can be provided to supply zero products outputfrom the selected pulse shape filters 618 in order to block the Ycomponent of a particular subcarrier or, if non-zero coefficients areprovided to the multiplier circuits instead, generate the opticalsubcarrier.

Thus, the above examples illustrate mechanisms by which the opticalsubcarriers can be selectively blocked from or added to the output ofthe transmitter 202. Since the DSPs and optical circuitry provided insecondary node transmitters 304 can be similar to those of the primarynode transmitter 202, the processes and circuitry described above can beprovided, for example, in the secondary node transmitters 304 toselectively add and remove optical subcarriers SC from the outputs ofthe secondary node transmitters. Moreover, the circuitry described abovein connection with FIGS. 6B and/or 6C can be configured such that afirst number of optical subcarriers are output from the transmitter (ineither the primary node 110 or the secondary node 112) during a firstperiod of time based on initial capacity requirements. Later, during asecond period of time, a second number of optical subcarriers can beoutput from the transmitters based on capacity requirements differentfrom the first capacity requirements.

The optical subcarriers SC0 to SC19 can be provided to secondary nodes112 in FIG. 1. An example of the receiver circuit 302 in one of thesecondary nodes 112 will be described next with reference to FIG. 7A.

As shown in FIG. 7A, the optical receiver 302 can include an Rx opticsand A/D block 700, which, in conjunction with the DSP 750, can carry outcoherent detection. The block 700 can include a polarization splitter(PBS) 705 with a first output 705-1 and a second output 705-2, a localoscillator (LO) laser 710, 90 degree optical hybrids or mixers 720-1 and720-2 (referred to generally as hybrid mixers 720 and individually as ahybrid mixer 720), detectors 730-1 and 730-2 (referred to generally asdetectors 730 and individually as a detector 730, each including eithera single photodiode or balanced photodiode), AC coupling capacitors732-1 and 732-2, transimpedance amplifiers/automatic gain controlcircuits TIA/AGC 734-1 and 734-2, ADCs 740-1 and 740-2 (referred togenerally as ADCs 740 and individually as an ADC 740).

The polarization beam splitter (PBS) 705 cam include a polarizationsplitter that receives an input polarization multiplexed optical signalincluding the optical subcarriers SC0 to SC19 supplied by the opticalfiber link 701, which may be, for example, an optical fiber segment aspart of one of optical communication paths 113-k to 113-m noted above.The PBS 705 can split the incoming optical signal into the two X and Yorthogonal polarization components. The Y component can be supplied to apolarization rotator 706 that rotates the polarization of the Ycomponent to have the X polarization. The hybrid mixers 720 can combinethe X and rotated Y polarization components with light from the localoscillator laser 710 (e.g., a tunable laser). For example, the hybridmixer 720-1 can combine a first polarization signal (e.g., the componentof the incoming optical signal having a first or X (TE) polarizationoutput from a first PBS port) with light from the local oscillator 710,and the hybrid mixer 720-2 can combine the rotated polarization signal(e.g., the component of the incoming optical signal having a second or Y(TM) polarization output from a second PBS port) with the light from thelocal oscillator 710. In some implementations, the polarization rotator790 can be provided at the PBS output to rotate Y component polarizationto have the X polarization.

The detectors 730 can detect mixing products output from the opticalhybrids to form corresponding voltage signals, which are subject to ACcoupling by the capacitors 732-1 and 732-1, as well as amplification andgain control by the TIA/AGCs 734-1 and 734-2. The outputs of theTIA/AGCs 734-1 and 734-2 and the ADCs 740 can convert the voltagesignals to digital samples. For example, two detectors (e.g.,photodiodes) 730-1 can detect the X polarization signals to form thecorresponding voltage signals, and a corresponding two ADCs 740-1 canconvert the voltage signals to digital samples for the firstpolarization signals after amplification, gain control and AC coupling.Similarly, two detectors 730-2 can detect the rotated Y polarizationsignals to form the corresponding voltage signals, and a correspondingtwo ADCs 740-2 can convert the voltage signals to digital samples forthe second polarization signals after amplification, gain control and ACcoupling. The RX DSP 750 can process the digital samples associated withthe X and Y polarization components to output data associated with oneor more optical subcarriers within a group of optical subcarriers SC0 toSC19 encompassed by the bandwidth (e.g., one of the bandwidths BWj, BWk,BW1, and BWm) associated with the secondary node housing the particularDSP 750. For example, as shown in FIG. 4, the optical subcarriers SC0 toSC8 are within a bandwidth BSj, and such optical subcarriers can beprocessed by the receiver in the secondary node 112-j. However, theoptical subcarriers SC5 to SC13 within a bandwidth BWk can be processedby the receiver in the secondary node 112-k. That is, the bandwidths BWjand BWk overlap, such that the optical subcarriers within the overlappedportions of these bandwidths, namely, the optical subcarriers SC5 toSC8, will be processed by the receivers in both the secondary node 112-jand the secondary node 112-k. If the data associated with these opticalsubcarriers is intended to be output from the secondary node 112-k,switch circuits can be provided to selectively output such data at thesecondary node 112-k but not from the secondary node 112-j.

While FIG. 7A shows the optical receiver 302 as including a particularnumber and arrangement of components, in some implementations, theoptical receiver 302 can include additional components, fewercomponents, different components, or differently arranged components.The number of detectors 730 and/or ADCs 740 can be selected to implementan optical receiver 302 that is capable of receiving a polarizationmultiplexed signal. In some instances, one of the components illustratedin FIG. 7A can carry out a function described herein as being carriedout by another one of the components illustrated in FIG. 7A.

In order to select a particular optical subcarrier or group of opticalsubcarriers at a secondary node 112, the local oscillator 710 can betuned to output light having a wavelength or frequency relatively closeto the selected optical subcarrier wavelength(s) to thereby cause abeating between the local oscillator light and the selected opticalsubcarrier(s). Such beating will either not occur or will besignificantly attenuated for the other non-selected subcarriers so thatdata carried by the selected optical subcarrier(s) is detected andprocessed by the DSP 650.

As noted above, each of the secondary nodes 112 can have a smallerbandwidth than the bandwidth associated with the primary node 110. Theoptical subcarriers encompassed by each of the secondary nodes can bedetermined by the frequency of the local oscillator laser 710 in thesecondary node receiver 302. For example, as shown in FIG. 7B, abandwidth BWj associated with the secondary node 112-j can be centeredabout the local oscillator frequency fLOj, a bandwidth BWk associatedwith the secondary node 112-k can be centered about the local oscillatorfrequency fLOk, a bandwidth BW1 associated with the secondary node 112-1can be centered about the local oscillator frequency fLOl, and abandwidth BWm associated with the secondary node 112-m can be centeredabout the local oscillator frequency fLOm. Accordingly, each of thebandwidth BWj to BWm can shift depending on the frequency of each of thesecondary node local oscillator lasers 710. Tuning the local oscillatorfrequency, for example, by changing the temperature of the localoscillator laser 710 can result in corresponding shifts in the bandwidthto encompass a different group of optical subcarriers than were detectedprior to such bandwidth shift. The temperature of the local oscillatorlaser 710 can be controlled with a thin film heater, for example,provided adjacent to the local oscillator laser or to portions of thelocal oscillator laser such as the mirror sections. Alternatively, thelocal oscillator laser can be frequency tuned by controlling the currentsupplied to the laser. The local oscillator laser 710 can be asemiconductor laser, such as a distributed feedback laser or adistributed Bragg reflector laser.

In some implementations, the maximum bandwidth or number of opticalsubcarriers that can be received, detected, and processed by a secondarynode receiver 302, can be restricted based on hardware limitations ofthe various circuit components in receiver 302, and, therefore may befixed. Accordingly, the bandwidth associated with each of the secondarynodes 112 can may be less than a bandwidth BW-P associated with theprimary node 110. Further, the number of secondary nodes can be greaterthan the number of optical subcarriers output from the primary node 110.In addition, the number of upstream optical subcarriers received by theprimary node 110 can be equal to the number of optical subcarrierstransmitted by the primary node 110 in the upstream direction.Alternatively, the number of optical subcarriers transmitted in theupstream direction collectively by the secondary nodes 112 can less thanor greater than the number of downstream optical subcarriers output fromthe primary node. Further, in some implementations, one or more of thesecondary nodes 112 can output a single optical subcarrier.

As shown in FIG. 7B and discussed above, the bandwidths associated withthe secondary nodes 112 can overlap, such that certain opticalsubcarriers can be detected by multiple secondary nodes 112. If the dataassociated with such optical subcarriers is intended for one of thosesecondary nodes, but not the other, switch circuitry can be provided inthe secondary nodes to output the data selectively at the intendedsecondary node but not the others.

For example, as further shown in FIG. 7A, the switches or circuits SW-0to SW-8 can be provided at the output of the DSP 750 to selectivelyoutput the data detected from the received optical subcarriers based ona respective one of control signals CNT-0 to CNT-8 output from thecontrol circuit 771 (see FIG. 7C), which, like the control circuit 571,can include a microprocessor, FPGA, or other processor circuit. Controlsignals can designate the output of each respective switch. Accordingly,if data carried by predetermined subcarriers is intended to be output ata particular secondary node 112, the switches SW at that secondary nodecan be configured, based on the received control signals CNT, to supplythe desired data, but block data not intended for that node. In someimplementations, at least some of the switches (e.g., SW-0 to SW-8, asshown in FIG. 7A) can be omitted, such that data stream are outputdirectly from the Rx DSP 750.

FIG. 8 illustrates exemplary components of the receiver digital signalprocessor (DSP) 750. As noted above, the analog-to-digital (A/D)circuits 740-1 and 740-2 (FIG. 7A) output digital samples correspondingto the analog inputs supplied thereto. In some implementations, thesamples may be supplied by each A/D circuit at a rate of 64 GSamples/s.The digital samples correspond to symbols carried by the X polarizationof the optical subcarriers and may be represented by the complex numberXI+jXQ. The digital samples may be provided to the overlap and savebuffer 805-1, as shown in FIG. 8. The FFT component or circuit 810-1 canreceive the 2048 vector elements, for example, from the overlap and savebuffer 805-1 and convert the vector elements to the frequency domainusing, for example, a fast Fourier transform (FFT). The FFT component810-1 can convert the 2048 vector elements to 2048 frequency components,each of which can be stored in a register or “bin” or other memory, as aresult of carrying out the FFT.

The frequency components then can be demultiplexed by the demultiplexer811-1, and groups of such components can be supplied to a respective oneof the chromatic dispersion equalizer circuits CDEQ 812-1-0 to 812-1-8,each of which may include a finite impulse response (FIR) filter thatcorrects, offsets or reduces the effects of, or errors associated with,chromatic dispersion of the transmitted optical subcarriers. Each of theCDEQ circuits 812-1-0 to 812-1-8 supplies an output to a correspondingpolarization mode dispersion (PMD) equalizer circuit 825-0 to 825-8(which individually or collectively may be referred to as PMB equalizercircuits 825).

Digital samples output from the A/D circuits 840-2 associated with Ypolarization components of optical subcarrier SC1 can be processed in asimilar manner to that of digital samples output from the A/D circuits840-1 and associated with the X polarization component of each opticalsubcarrier. In particular, the overlap and save buffer 805-2, the FFT810-2, the demultiplexer 811-2, and the CDEQ circuits 812-2-0 to 812-2-8can have a similar structure and operate in a similar fashion as thebuffer 805-1, the FFT 810-1, the demultiplexer 811-1, and the CDEQcircuits 812-1-0 to 812-1-8, respectively. For example, each of the CDEQcircuits 812-2-0 to 812-8 can include an FIR filter that corrects,offsets, or reduces the effects of, or errors associated with, chromaticdispersion of the transmitted optical subcarriers. In addition, each ofthe CDEQ circuits 812-2-0 to 812-2-8 provide an output to acorresponding one of the PMDEQ 825-0 to 825-8.

As further shown in FIG. 8, the output of one of the CDEQ circuits, suchas the CDEQ 812-1-0 can be supplied to a clock phase detector circuit813 to determine a clock phase or clock timing associated with thereceived subcarriers. Such phase or timing information or data can besupplied to the ADCs 740-1 and 740-2 to adjust or control the timing ofthe digital samples output from the ADCs 740-1 and 740-2.

Each of the PMDEQ circuits 825 can include another FIR filter thatcorrects, offsets or reduces the effects of, or errors associated with,PMD of the transmitted optical subcarriers. Each of the PMDEQ circuits825 can supply a first output to a respective one of the IFFT componentsor circuits 830-0-1 to 830-8-1 and a second output to a respective oneof the IFFT components or circuits 830-0-2 to 830-8-2, each of which canconvert a 256-element vector, in this example, back to the time domainas 256 samples in accordance with, for example, an inverse fast Fouriertransform (IFFT).

Time domain signals or data output from the IFFT 830-0-1 to 830-8-1 aresupplied to a corresponding one of the Xpol carrier phase correctioncircuits 840-1-1 to 840-8-1, which can apply carrier recovery techniquesto compensate for the X polarization transmitter (e.g., the laser 508)and the receiver (e.g., the local oscillator laser 710) linewidths. Insome implementations, each carrier phase correction circuit 840-1 to840-8-1 can compensate or correct for frequency and/or phase differencesbetween the X polarization of the transmit signal and the X polarizationof light from the local oscillator 700 based on an output of the Xpolcarrier recovery circuit 840-0-1, which performs carrier recovery inconnection with one of the optical subcarriers based on the outputs ofthe IFFT 830-01. After such X polarization carrier phase correction, thedata associated with the X polarization component may be represented assymbols having the complex representation xi+j*xq in a constellation,such as a QPSK constellation or a constellation associated with anothermodulation formation, such as an m-quadrature amplitude modulation(QAM), m being an integer. In some implementations, the taps of the FIRfilter included in one or more of the PMDEQ circuits 825 can be updatedbased on the output of at least one of the carrier phase correctioncircuits 840-0-1 to 840-8-01.

In a similar manner, time domain signals or data output from the IFFT830-0-2 to 830-8-2 are supplied to a corresponding one of the Ypolcarrier phase correction circuits 840-0-2 to 840-8-2, which maycompensate or correct for the Y polarization transmitter (e.g., thelaser 508) and the receiver (e.g., the local oscillator laser 710)linewidths. In some implementations, each carrier phase correctioncircuit 840-0-2 to 840-8-2 also can correct or compensate for frequencyand/or phase differences between the Y polarization of the transmitsignal and the Y polarization of light from the local oscillator 710.After such Y polarization carrier phase correction, the data associatedwith the Y polarization component can be represented as symbols havingthe complex representation yi+j*yq in a constellation, such as a QPSKconstellation or a constellation associated with another modulationformation, such as an m-quadrature amplitude modulation (QAM), m beingan integer. In some implementations, the output of one of the circuits840-0-2 to 840-8-2 can be used to update the taps of the FIR filterincluded in one or more of the PMDEQ circuits 825 instead of, or inaddition to, the output of at least one of the carrier recovery circuits840-0-1 to 840-8-1.

As further shown in FIG. 8, the output of carrier recovery circuits(e.g., the carrier recovery circuit 840-0-1) also can be supplied to thecarrier phase correction circuits 840-1-1 to 840-8-1 and 840-0-2 to840-8-2, whereby the phase correction circuits can determine orcalculate a corrected carrier phase associated with each of the receivedoptical subcarriers based on one of the recovered carriers, instead ofproviding multiple carrier recovery circuits, each of which isassociated with a corresponding optical subcarrier. The equalizer,carrier recovery, and clock recovery can be further enhanced byutilizing the known (training) bits that may be included in controlsignals CNT, for example by providing an absolute phase referencebetween the transmitted and local oscillator lasers.

Each of the symbols-to-bits circuits or components 845-0-1 to 845-8-1can receive the symbols output from a corresponding one of the circuits840-0-1 to 840-8-1 and map the symbols back to bits. For example, eachof the symbol-to-bits components 845-0-1 to 845-8-1 can map one Xpolarization symbol, in a QPSK or m-QAM constellation, to Z bits, whereZ is an integer. For dual-polarization QPSK modulated subcarriers, Z isfour. Bits output from each of the components 845-0-1 to 845-8-1 areprovided to a corresponding one of the FEC decoder circuits 860-0 to860-8.

Y polarization symbols are output form a respective one of the circuits840-0-2 to 840-8-2, each of which has the complex representation yi+j*yqassociated with data carried by the Y polarization component. Each Ypolarization, like the X polarization symbols noted above, can beprovided to a corresponding one of the bit-to-symbol circuits orcomponents 845-0-2 to 845-8-2, each of which has a similar structure andoperates in a similar manner as the symbols-to-bits components 845-0-1to 845-8-1. Each of the circuits 845-0-2 to 845-8-2 can provide anoutput to a corresponding one of the FEC decoder circuits 860-0 to860-8.

Each of the FEC decoder circuits 860 can remove errors in the outputs ofthe symbol-to-bit circuits 845 using, for example, forward errorcorrection. Such error corrected bits, which can include user data foroutput from the secondary nodes 112, can be supplied to a correspondingone of the switch circuits SW-0 to SW-8. As noted above, the switchcircuits SW-0 to SW-8 in each secondary node 112 can selectively supplyor block data based on whether such data is intended to be output fromthe secondary node. In addition, if one of the received opticalsubcarriers' control information (CNT), such as information identifyingthe switches SW that output data and other switches SW that block data,the control information may be output from one of the switches and,based on such control information, the control circuit 771 in thesecondary nodes to generate the control signals CNT.

In some implementations, data can be blocked from output from the DSP750 without the use of the switches SW-0 to SW-8. As an example, zero(0) or other predetermined values can be stored in frequency binsassociated with the blocked data, as well as the optical subcarriercorresponding to the blocked data. Further, as described above,processing of such zeroes or predetermined data by circuitry in the DSP750 will result in null or zero data outputs, for example, from acorresponding one of the FEC decoders 860. The switch circuits providedat the outputs of the FFTs 810-1 and 810-2, like the switch circuits SWdescribed above in FIG. 6B, can be provided to selectively insert zeroesor predetermined values for selectively blocking corresponding outputdata from the DSP 750. Such switches also can be provided at the outputof or within the demultiplexers 811-1 and 811-2 to selectively supplyzero or predetermined values.

In another example, zeroes (0s) can be inserted in the chromaticdispersion equalizer (CDEQ) circuits 812 associated with both the X andY polarization components of each optical subcarrier. In particular,multiplier circuits (provided in corresponding butterfly filtercircuits), like multiplier circuits M described above, can selectivelymultiply the inputs to the CDEQ circuit 812 by either zero or a desiredcoefficient. As discussed above in connection with FIG. 6C,multiplication by a zero generates a zero product. When such zeroproducts are further processed by corresponding circuitry in the DSP 750(e.g., corresponding IFFTs 1230, carrier phase correction components840, symbol-to-bits components 845, and FEC decoder), a correspondingoutput of the DSP 750 will also be zero. Accordingly, data associatedwith an optical subcarrier received by a secondary node receiver 112,but not intended for output from that receiver, can be blocked.

However, if capacity requirements change and such previously blockeddata is to be output from a given secondary node receiver DSP 750,appropriate coefficients can be supplied to the multiplier circuits,such that at least some of the inputs thereto are not multiplied byzero. Upon further processing, as noted above, data associated with theinputs to the multiplier circuits and corresponding to a particularoptical subcarrier is output from secondary node receiver DSP 750.

While FIG. 8 shows the DSP 750 as including a particular number andarrangement of functional components, in some implementations, the DSP750 can include additional functional components, fewer functionalcomponents, different functional components, or differently arrangedfunctional components.

In some implementations, a node (e.g., a primary node 110, as describedabove) can transmit data to multiple other nodes (e.g., multiplesecondary nodes 112, as described above) concurrently, such that similardata is “multicast” to multiple nodes at the same time. Upon receipt ofthe data, each of the nodes can selectively retain one or more portionsof the data (e.g., the portions of the data that are intended for thenode) and discard one or more other portions of the data (e.g., theportions of the data that are intended for other nodes). In someimplementations, data can be transmitted as one or more optical carriers(e.g., as described above).

Further, as described above, at least some of the secondary nodes 112can include components that have different (e.g., lower) capabilitiesthan the components included in primary node 110. For example, thebandwidth or the data capacity of at least some of the secondary nodes112 can be less than that associated with the primary node 110, suchthat the capacity associated with each of those secondary nodes 112 isless than that of the primary node 110. Accordingly, the primary node100 can transmit data to each of those secondary nodes 112 according toa higher bit rate (e.g., using a higher capacity transceiver), and eachof those secondary nodes 112 can transmit data to the primary node 110according to a lower bit rate (e.g., using a lower capacitytransceiver). Accordingly, downstream data (e.g., from the primary node100 to the secondary nodes 112) is transmitted according to a largerpooled allocation of bandwidth, whereas upstream data (e.g., from eachof the secondary nodes 112 to the primary node 110) is transmittedaccording to respective smaller dedicated allocations of bandwidth.

As an example, FIG. 9A shows a primary node 110 interconnected tomultiple secondary nodes 112 a-112 d via respective opticalcommunication paths 111. The primary node 110 includes a transceiver 900having a first capacity (e.g., capable of transmitting data according toa first bit rate or bandwidth). Each of the secondary nodes 112 a-112 dincludes a respective transceiver 902 a-902 d having a second capacity(e.g., capable of transmitting data according to a second bit rate orbandwidth). In some implementations, the transceivers 900 and 902 a-902d can be implemented in a similar manner as the transmitters 202 and 302and/or the receivers 204 and 304 described above.

The transceiver 900 has a higher capacity than that of each of thetransceivers 902 a-902 d. As an example, the transceiver 900 cantransmit data to each of the transceivers 902 a-902 d concurrently at abit rate of 100 Gbit/s (e.g., multicast data at a bit rate of 100Gbit/s), whereas each of the transceivers 902 a-902 d can transmit dataat a bit rate of 25 Gbit/s. Upon receipt of the data, each of the secondnodes 902 a-902 d can selectively retain one or more portions of thedata (e.g., the portions of the data that are intended for thatsecondary node) and discard one or more other portions of the data(e.g., the portions of the data that are intended for other secondarynodes).

The optical communication paths 111 can be similar to those describedabove (e.g., with respect to FIGS. 1 and 2). For instance, each of theoptical communication paths 111 can include or more segments of opticalfiber, optical switches, optical amplifiers, reconfigurable add-dropmultiplexers (ROADMs), and/or other optical fiber communicationequipment. As an illustrative example, FIG. 9B shows example physicalinterconnections between the primary node 110 and the secondary nodes112 a-112 d via the optical communication paths 111. The opticalcommunication paths 111 includes several lengths of optical fiber 904,and several optical splitters 906 a-906 c. The optical fiber carriesoptical signals from the primary node 110 to an input of the firstoptical splitter 906 a, which splits the optical signal into tworespective lengths of optical fiber at its output. In turn, each opticalsignal is further split by the second optical splitter 906 b or thethird optical splitter 906 c (e.g., according to a nested or “tree”topology). Accordingly, the original optical signal output from theprimary node 110 is ultimately split into four optical signals, each ofwhich is delivered to a respective one of the secondary nodes 112 a-112d. Although an example network topology is shown and described, this ismerely an illustrative example. In practice, other network topologiesare also possible, depending on the implementation.

In some implementations, one node can transmit data to and receive datafrom another node using multiple different links. As an example, FIG.10A shows a first node 1000 a and a second node 1000 b. The first node1000 a includes two respective transceivers 1002 a and 1002 b, and thesecond node 1000 b includes two respective transceivers 1004 a and 1004b. In some implementations, the transceivers 1002 a, 1002 b, 1004 a, and1004 b can be implemented in a similar manner as the transmitters 202and 302 and/or the receivers 204 and 304 described above.

The transceivers 1002 a and 1004 a have a higher capacity than that ofthe transceivers 1002 b and 1004 b. As an example, the transceivers 1002a and 1004 a can transmit data to the transceivers 1002 b and 1004 b,respectively, according to a first bit rate (e.g., 100 Gbit/s), and thetransceivers 1002 b and 1004 b can transmit data according to a secondbit rate less than the first bit rate (e.g., 50 Gbit/s). Accordingly,data can be transmitted from the transceiver 1002 a to the transceiver1004 b according to a larger pooled allocation of bandwidth (e.g., 100Gbit/s, which can be shared among multiple recipient nodes throughmulticasting), and data can be transmitted from the transceiver 1002 bto the transceiver 1004 a according to a smaller dedicated allocation ofbandwidth (e.g., 50 Gbit/s).

As described above, in some implementations, one node can transmit datato and receive data from multiple other nodes concurrently. As anexample, FIG. 10B shows three nodes 1006 a-1006 c. The first node 1006 aincludes three respective transceivers 1008 a-1008 c, the secondary node1006 b includes two respective transceivers 1010 a and 1010 b, and thethird node 1006 c includes two respective transceivers 1012 a and 1012b. In some implementations, the transceivers 1008 a, 1008 b, 1010 a,1010 b, 1012 a, and 1012 b can be implemented in a similar manner as thetransmitters 202 and 302 and/or the receivers 204 and 304 describedabove.

The transceivers 1008 a, 1010 a, and 1012 a have a higher capacity thanthat of the transceivers 1008 b, 1008 c, 1010 b, and 1012 b. As anexample, the transceivers 1008 a, 1010 a, and 1012 a can transmit dataaccording to a first bit rate (e.g., 100 Gbit/s), and the transceivers1008 b, 1008 c, 1010 b, and 1012 b can transmit data according to asecond bit rate less than the first bit rate (e.g., 50 Gbit/s). Further,each of the transceivers 1008 a, 1010 a, and 1012 a can multicast datato multiple other transceivers concurrently. Accordingly, the node 1006a is interconnected to each of the other nodes 1006 b and 1006 c via tworespective links. For each link, data is transmitted in a downstreamdirection (e.g., from a high capacity transceiver to a low capacitytransceiver(s)) according to a larger pooled allocation of bandwidth(e.g., 100 Gbit/s, which can be shared among multiple recipient nodesthrough multicasting), and data is transmitted in the upstream directionaccording to a smaller dedicated allocation of bandwidth (e.g., 50Gbit/s).

In some implementations, data can be multicast in two multipletransceivers in a single node. As an example, FIG. 10C shows two nodes1014 a and 1014 b. The first node 1014 a includes three respectivetransceivers 1016 a-1016 c, the second node 1014 b includes threerespective transceivers 1018 a-1018 c. In some implementations, thetransceivers 1016 a-1016 c and 1018 a-1018 c can be implemented in asimilar manner as the transmitters 202 and 302 and/or the receivers 204and 304 described above.

The transceivers 1016 a and 1018 a have a higher capacity than that ofthe transceivers 1016 b, 1016 c, 1018 b, and 1018 c. As an example, thetransceivers 1016 a and 1018 a can transmit data according to a firstbit rate (e.g., 100 Gbit/s), and the transceivers 1016 b, 1016 c, 1018b, and 1018 c can transmit data according to a second bit rate less thanthe first bit rate (e.g., 50 Gbit/s). Further, each of the transceivers1016 a and 1018 a can multicast data to multiple other transceiversconcurrently. Accordingly, the nodes 1014 a and 1014 b areinterconnected to each other via three links. For each link, data istransmitted in a downstream direction (e.g., from a high capacitytransceiver to a low capacity transceiver(s)) according to a largerpooled allocation of bandwidth (e.g., 100 Gbit/s, which is sharedbetween two destination transceivers nodes through multicasting), anddata is transmitted in the upstream direction according to a smallerdedicated allocation of bandwidth (e.g., 50 Gbit/s).

As another example, FIG. 10D shows three nodes 1020 a-1020 c. The firstnode 1020 a includes five respective transceivers 1022 a-1022 e, thesecond node 1020 b includes three respective transceivers 1024 a-1024 c,and the third node 1020 c includes three respective transceivers 1026a-10246. In some implementations, the transceivers 1022 a-1022 e, 1024a-1024 c, and 1026 a-1024 c can be implemented in a similar manner asthe transmitters 202 and 302 and/or the receivers 204 and 304 describedabove.

The transceivers 1022 a, 1024 a, and 1026 a have a higher capacity thanthat of the transceivers 1022 b-1022 e, 1024 b, 1024 c, 1026 b, and 1024c. As an example, the transceivers 1022 a, 1024 a, and 1026 a cantransmit data according to a first bit rate (e.g., 100 Gbit/s), and thetransceivers 1022 b-1022 e, 1024 b, 1024 c, 1026 b, and 1024 c cantransmit data according to a second bit rate less than the first bitrate (e.g., 50 Gbit/s). Further, each of the transceivers 1022 a, 1024a, and 1026 a can multicast data to multiple other transceiversconcurrently. Accordingly, the node 1020 a is interconnected with eachof the nodes 1020 b and 1020 c via three respective links. For eachlink, data is transmitted in a downstream direction (e.g., from a highcapacity transceiver to a low capacity transceiver(s)) according to alarger pooled allocation of bandwidth (e.g., 100 Gbit/s, which is sharedbetween two destination transceivers nodes through multicasting), anddata is transmitted in the upstream direction according to a smallerdedicated allocation of bandwidth (e.g., 50 Gbit/s).

One or more of the features described herein can be implemented, forexample, in a datacenter environment. As an example, FIG. 11 shows asystem 1100 for routing data in a datacenter. The system 1100 includes Ncore switches CORE 1 to CORE N forming the backbone of a communicationsnetwork. Further, the system 1100 includes M top of rack (ToR) switchesToR 1 to ToR M interconnected with the core switches CORE 1 to CORE viarespective optical communication paths 111, forming the edges or “top”of the communications network. Further, system includes several servercomputers interconnected with the ToR switches ToR 1 to ToR M viarespective optical communication paths 111. In some implementations, thesystem 1100 can be, at least in part, a local area network (LAN), suchas an Ethernet LAN.

During operation of the system 1100, the core switches CORE 1 to CORE Nreceive data from a wide area network (WAN), such as the Internet, androute data to one or more of the server computers via the ToR switchesToR 1 to ToR M. Further, the server computers can communicate with oneanother and/or transmit data to the WAN via the ToR switches ToR 1 toToR M and/or the core switches CORE 1 to CORE N.

The system 1100 can be implemented using one or more high capacitytransceivers and one or more low capacity transceivers, in a similarmanner to that described above. This enables traffic to be transmittedin certain directions according to a pooled allocation of bandwidth(e.g., shared among multiple nodes of the network to alleviatecongestion), while also enabling traffic to be transmitted in certainother directions according to smaller dedicated allocations ofbandwidth. Further, this enables a network to be deployed and maintainedin a more cost efficient manner (e.g., compared to using solely highcapacity transceivers across the entirety of the network). In someimplementations, the transceivers can be implemented in a similar manneras the transceivers described above with respect to FIGS. 9 and 10A-10D.

To illustrate, FIG. 12A shows example interconnections between a ToRswitch and the server computers in the system 1100. In this example, theToR switch includes number of low capacity transceivers 1102 (e.g., 64)and a number of high capacity transceivers 1104 (e.g., 8). In someimplementations, each of the high capacity transceivers 1104 can beconfigured to transmit data according to a maximum bit rate of 800Gbit/s (e.g., using 8 groups of optical subcarriers, each having abandwidth allocation of 100 Gbit/s). Further, the low capacitytransceivers can be configured to transmit data according to a maximumbit rate of 100 Gbit/s each (e.g., using 2 groups of optical high, eachhaving a bandwidth allocation of 50 Gbit/s). In this example, each ofthe high capacity transceivers 1104 is communicatively coupled to adifferent respective group of the server computers (e.g., groups of 64server computers each). Further, each optical subcarrier of the highcapacity transceiver 1104 is assigned to a different subgroup of theserver computers (e.g., subgroups of 8 server computers each). Further,each server computer includes a respective low capacity transceiver(e.g., a transceiver capable of transmitting data according to a bitrate of 12.5 Gbit/s). For ease of illustration, the low capacitytransceivers of the server computers are not shown separately in FIG.12A.

Further, the high capacity transceivers 1104 are configured to multicastdata to its respective subgroup of server computers. For example, totransmit data to one of the server computers in Subgroup 1 of Group 1,the high capacity transceiver 1104 that is coupled to Group 1 can selectthe optical subcarrier corresponding to Subgroup 1 (e.g., an opticalsubcarrier having a bandwidth allocation of 100 Gbit/s), and multicastthe data to each of the server computers in Subgroup 1. Upon receivingthe multicasted data, each of the server computers in Subgroup 1examines the data to determine whether it is the intended destinationfor the data (e.g., by inspecting a destination data field in the dataand/or determining whether the data is included in an optical subcarrierto which the server computer has been assigned). If so, the servercomputer retains the data. If not, the server computer discards thedata. Accordingly, each of the server computers shares a common pool ofallocated bandwidth (in this example, 100 Gbit/s) with other servercomputers when receiving data from the ToR switch.

Further, each of the server computers can transmit data to the ToRswitch using its respective low capacity transceiver according to adedicated optical subcarrier (e.g., an optical subcarrier having abandwidth allocation of 12.5 Gbit/s). Accordingly, each of the servercomputers is guaranteed a particular allotment of bandwidth (in thisexample, 12.5 Gbit/s), regardless of the bandwidth utilized by other theserver computers.

In the example shown in FIG. 12A, the ToR switch includes 8 highcapacity transceivers 1104, where each high capacity transceiver 1104 iscoupled to 8 groups of 64 server computers, and where each group ofserver computers is further divided into 8 subgroups of 8 servercomputers each. Further, each of the high capacity transceivers 1104 isconfigured to transmit data according to a maximum bit rate of 800Gbit/s (e.g., using 8 groups of optical subcarriers, each having abandwidth allocation of 100 Gbit/s), and the low capacity transceiversare configured to transmit data according to a maximum bit rate of 100Gbit/s each (e.g., using 2 groups of optical high, each having abandwidth allocation of 50 Gbit/s). However, different configurationsare also possible. For example, the ToR switch can include any number ofhigh capacity transceivers 1104, where each high capacity transceiver1104 is coupled to any number of groups of any number of servercomputers, and where each group of server computers is further dividedinto any number of subgroups of any number of server computers each.Further, the high capacity transceivers 1104 and the low capacitytransceivers can be configured to transmit data according to differentmaximum bit rates, using different numbers of optical subcarriers and/ordifferent allocations of bandwidth.

FIG. 12B shows example interconnections between a core switch andmultiple ToR switches in the system 1100. In this example, the coreswitch number of first high capacity transceivers 1106 (e.g., 8) and anumber of second high capacity transceivers 1108 (e.g., 8). In someimplementations, each of the first and second high capacity transceivers1108 can be configured to transmit data according to a maximum bit rateof 800 Gbit/s (e.g., using 8 groups of optical subcarriers, each havinga bandwidth allocation of 100 Gbit/s).

In this example, the first high capacity transceivers 1106 arecommunicatively coupled to the WAN. For example, the first high capacitytransceivers 1106 can be used to transmit data to the WAN from one ormore of the server computers and/or the ToR switches, and to receivedata from the WAN intended for one or more of the server computersand/or the ToR switches.

Further, in this example, each of the second high capacity transceivers1108 is communicatively coupled to a different respective group of theToR switches (e.g., groups of 32 ToR switches each) via the low capacitytransceivers 1102 (e.g., as shown in FIG. 12A). Further, each opticalsubcarrier of the second high capacity transceiver 1108 is assigned to adifferent subgroup of the ToR switches (e.g., subgroups of 4 ToRswitches each). Further, as described above, each ToR switch includes arespective low capacity transceiver 1102 (e.g., a transceiver capable oftransmitting data according to a bit rate of 12.5 Gbit/s).

Further, two links are established between the core switch and each ToRswitch. For example, the first four high capacity switches 1108 arecoupled to different respective groups of the ToR switches. Further, thesecond four high capacity switches 1108 are also coupled to respectivegroups of the same ToR switches, such that two links are establishedbetween the core switch and each ToR switch.

Further, the high capacity transceivers 1108 are configured to multicastdata to its respective subgroup of ToR switches. For example, totransmit data to one of the ToR switches in Subgroup 1 of Group 1, thehigh capacity transceivers 1108 that are coupled to Group 1 can selectthe optical subcarrier(s) corresponding to Subgroup 1 (e.g., opticalsubcarriers each having a bandwidth allocation of 100 Gbit/s), andmulticast the data to each of the ToR switches in Subgroup 1. Uponreceiving the multicasted data, each of the ToR switches in Subgroup 1examines the data to determine whether it is the intended destinationfor the data (e.g., by inspecting a destination data field in the dataand/or determining whether the data is included in an optical subcarrierto which the ToR switch has been assigned). If so, the ToR switchretains the data. If not, the ToR switch discards the data. Accordingly,each of the ToR switches shares a common pool of allocated bandwidth (inthis example, 200 Gbit/s across two links) with other ToR switches whenreceiving data from the core switch.

Further, each of the ToR switches can transmit data to the core switchusing its respective low capacity transceivers according to dedicatedoptical subcarrier(s) (e.g., optical subcarriers having a bandwidthallocation of 12.5 Gbit/s). Accordingly, each of the server computers isguaranteed a particular allotment of bandwidth (in this example, 25Gbit/s across two links), regardless of the bandwidth utilized by otherthe server computers.

In the example shown in FIG. 12B, the core switch includes 8 highcapacity transceivers 1108, where each high capacity transceiver 1108 iscoupled to 4 groups of 128 ToR switches (with two links each between thecore switch and each ToR switch), and where each group of ToR switchesis further divided into 8 subgroups of 4 ToR switches each. Further,each of the first and second high capacity transceivers 1108 areconfigured to transmit data according to a maximum bit rate of 800Gbit/s (e.g., using 8 groups of optical subcarriers, each having abandwidth allocation of 100 Gbit/s). However, different configurationsare also possible. For example, the core switch can include any numberof high capacity transceivers 1108, where each high capacity transceiver1108 is coupled to any number of groups of any number of ToR switches,and where each group of ToR switches is further divided into any numberof subgroups of any number of ToR switches each. Further, the first andsecond high capacity 1108 can be configured to transmit data accordingto different maximum bit rates, using different numbers of opticalsubcarriers and/or different allocations of bandwidth. Further still,any number of links can be established between the core switch and eachToR switch.

In the examples shown and described with respect to FIGS. 11, 12A, and12B, network nodes (e.g., core switches, ToR switches, and servercomputers) are arranged according to a nested or tree topology. Forexample, each core switch is coupled to one or more ToR switches, whichare in turn coupled to one or more server computers. However, this neednot always be the case. For instance, in some implementations, networknodes can be arranged according to a flat or mesh topology.

As an example, FIG. 13 shows a system 1300 having a mesh topology. Thesystem 1300 includes a number of nodes 1302 a-1302 i interconnected withone another via respective optical communication paths 111. In thisexample, each node 1302 a-1302 i includes a respective high capacitytransceiver (represented by a square) and several respective lowcapacity transceivers (represented by circles). The high capacitytransceivers can be configured to transmit data according to a first bitrate (e.g., 400 Gbit/s), whereas the low capacity transceivers can beconfigured to transmit data according to second bit rate that is lowerthan the first bit rate (e.g., 100 Gbit/s). In some implementations, thetransceivers can be implemented in a similar manner as the transceiversdescribed above with respect to FIGS. 9 and 10A-10D.

In this example, the high capacity transceiver of each of the nodes 1302a-1302 i is coupled to a low capacity transceiver of each of the othernodes 1302 a-1302 i, forming a symmetric mesh topology. Further, asdescribed above, the high capacity transceiver can multicast data toeach of the low capacity transceivers to which it is coupled, such thatdata is transmitted in a downstream direction (e.g., from a highcapacity transceiver to a low capacity transceiver(s)) according to alarger pooled allocation of bandwidth (e.g., 400 Gbit/s, which can beshared among the recipient nodes). Further, data is transmitted in theupstream direction according to a smaller dedicated allocation ofbandwidth (e.g., 100 Gbit/s).

As an example, the node 1302 a can transmit data to the node 1302 b bymulticasting the data to each of the nodes 1302 b-1302 i using its highcapacity transceiver (e.g., by transmitting the data using an opticalsubcarrier associated with each of the nodes). Upon receiving themulticasted data in their respective low capacity transceivers, each ofthe nodes 1302 b-1302 i examines the data to determine whether it is theintended destination for the data (e.g., by inspecting a destinationdata field in the data and/or determining whether the data is includedin an optical subcarrier to which the node has been assigned). If so,the node retains the data. If not, the node discards the data.Accordingly, each of the node shares a common pool of allocatedbandwidth (in this example, 400 Gbit/s) with other nodes when receivingdata.

In the example system 1300 shown in FIG. 13, the high capacitytransceiver of each of the nodes 1302 a-1302 i is coupled to a singlelow capacity transceiver of each of the other nodes 1302 a-1302 i.However, this need not always be the case. For example, in someimplementations, at least some of the high capacity transceivers can becoupled to multiple low capacity transceivers of another node.

As an example, FIG. 14 shows another system 1400 having a mesh topology.The system 1400 includes a number of nodes 1402 a-1402 e interconnectedwith one another via respective optical communication paths 111. In thisexample, each node 1402 a-1402 e includes a respective high capacitytransceiver (represented by a square) and several respective lowcapacity transceivers (represented by circles). The high capacitytransceivers can be configured to transmit data according to a first bitrate (e.g., 400 Gbit/s), whereas the low capacity transceivers can beconfigured to transmit data according to second bit rate that is lowerthan the first bit rate (e.g., 100 Gbit/s). In some implementations, thetransceivers can be implemented in a similar manner as the transceiversdescribed above with respect to FIGS. 9 and 10A-10D.

In this example, the high capacity transceiver of each of the nodes 1402a-1402 e is coupled to two respective low capacity transceivers of eachof the other nodes 1402 a-1402 e, forming a symmetric mesh topology.Further, as described above, the high capacity transceiver can multicastdata to each of the low capacity transceivers to which it is coupled,such that data is transmitted in a downstream direction (e.g., from ahigh capacity transceiver to a low capacity transceiver(s)) according toa larger pooled allocation of bandwidth (e.g., 400 Gbit/s, which can beshared among the recipient nodes). Further, data is transmitted in theupstream direction according to a smaller dedicated allocation ofbandwidth (e.g., 200 Gbit/s across two different links).

In the examples shown in FIGS. 12 and 13, nodes are interconnectedaccording to a symmetric topology (e.g., each node is interconnectedwith each other node in a similar manner). However, this need not alwaysbe the case. For instance, in some implementations, the nodes can beinterconnected according to an asymmetric topology. For example, atleast one node can be interconnected with only a subset of the othernodes, and not directly interconnected with another subset of the othernodes.

As an example, FIG. 15 shows another system 1500 having a mesh topology.The system 1500 includes a number of nodes 1502 a-1502 i interconnectedwith one another via respective optical communication paths 111. In thisexample, each node 1502 a-1502 i includes a respective high capacitytransceiver (represented by a square) and several respective lowcapacity transceivers (represented by circles). The high capacitytransceivers can be configured to transmit data according to a first bitrate (e.g., 400 Gbit/s), whereas the low capacity transceivers can beconfigured to transmit data according to second bit rate that is lowerthan the first bit rate (e.g., 100 Gbit/s). In some implementations, thetransceivers can be implemented in a similar manner as the transceiversdescribed above with respect to FIGS. 9 and 10A-10D.

In this example, the high capacity transceiver of the node 1502 a iscoupled to a low capacity transceiver of each of the other nodes 1502b-1502 i. Similarly, the high capacity transceiver of the node 1502 e iscoupled to a low capacity transceiver of each of the other nodes 1502a-1502 d and 1502 f-1502 i. However, the high capacity transceivers ofthe remaining nodes 1502 b-1502 d and 1502 f-1502 i are coupled to thelow capacity transceivers of only a subset of the other nodes.Accordingly, the nodes of the system 1500 form an asymmetric meshtopology (e.g., the interconnections between some nodes are differentfrom the interconnections between other nodes).

An asymmetric mesh topology may be preferable in some implementations.For example, certain nodes that transmit data to and/or receive datafrom a large number of other nodes (e.g., “primary” hubs) can beallocated more network resources (e.g., a greater number of links can bedeployed between the node and other nodes), whereas other nodes thattransmit data to and/or receive data from a fewer number of other nodes(e.g., “secondary” hubs) can be allocated fewer network resources (e.g.,a fewer number of links can be deployed between the node and othernodes). Accordingly, the network can be deployed and maintained in amore cost and/or time efficient manner. Nevertheless, a symmetric meshtopology can be used in at least some implementations (e.g., whennetwork traffic is not concentrated between a limited number of nodes).

In some implementations, an asymmetric mesh topology can be deployedbased on measured network traffic between each of the nodes (e.g.,network traffic transmitted using an existing communications network).One or more network links can be selectively deployed between particularnodes based on the measurements.

To illustrate, FIG. 16A shows another example system 1600 that includesa number of nodes 1602 a-1602 i interconnected with one another via acommunications network 1604 (e.g., a network having a symmetric meshtopology, a nested or tree topology, or any other topology).

The system 1600 also includes a traffic monitoring system 1606 that iscommunicatively coupled to the network 1604. The traffic monitoringsystem 1606 measures the network traffic that is transmitted to and fromeach of the nodes 1602 a-1602 i, and generates one or more utilizationmetrics based on the measurements. In some implementations, the trafficmonitoring system 1606 can generate utilization metrics indicating theamount of data (e.g., the data size of the network traffic) that istransmitted between nodes, the source of network traffic, thedestination of network traffic, the time that data was transmitted overthe network 1604, the frequency by which data is transmitted, theproportion of available network resources used in transferring the data,and/or any other information regarding the transmission of data over thenetwork 1604.

Further, the traffic monitoring system 1606 can rank the network trafficaccording to the utilization metrics. For instance, a higher utilizationmetric could signify that a particular portion of the network trafficrepresents a larger proportion of the total network traffic, whereas alower utilization metric could signify that a particular portion of thenetwork traffic represents a smaller proportion of the total networktraffic. In some implementations, network traffic can be groupedaccording to its source and destination, and different groups of networktraffic can be ranked relative to one another.

As an example, as shown in FIG. 16A, the traffic monitoring system 1606can generate a table 1608 ranking different groups of network trafficrelative to one another. In this example, network traffic between a Node1 (e.g., the node 1602 a) and a Node 5 (e.g., the node 1602 e) has beenassigned a utilization metric of 1 in the direction from Node 1 to Node5, and utilization metric of 0.23 in the direction from Node 5 to Node1; network traffic between a Node 1 (e.g., the node 1602 a) and a Node 3(e.g., the node 1602 c) has been assigned a utilization metric of 0.84in the direction from Node 1 to Node 3, and a utilization metric of 0.11in the direction from Node 3 to Node 1; network traffic between a Node 5(e.g., the node 1602 e) and a Node 8 (e.g., the node 1602 h) has beenassigned a utilization metric of 0.44 in the direction from Node 5 toNode 8, and a utilization metric of 0.05 in the direction from Node 8 toNode 5; network traffic between a Node 5 (e.g., the node 1602 e) and aNode 4 (e.g., the node 1602 d) has been assigned a utilization metric of0.33 in the direction from Node 5 to Node 4 and a utilization metric of0.23 in the direction from Node 4 to Node 5; and network traffic betweena Node 2 (e.g., the node 1602 b) and a Node 3 (e.g., the node 1602 c)has been assigned a utilization metric of 0.05 in the direction fromNode 2 to Node 3, and a utilization metric of 0.05 in the direction fromNode 3 to Node 2. Utilization metrics indicating the network trafficbetween each of the other nodes also can be generated.

When deploying the asymmetric network, the inclusion of network linksbetween the particular nodes can be prioritized over network linksbetween other nodes based on the rankings. Some or all of these networklinks can be links between high capacity transceivers and low capacitytransceivers, as described herein.

For instance, in this example, the network traffic from the Node 1(e.g., the node 1602 a) to a Node 5 (e.g., the node 1602 e) has thehighest ranking from among the groups of network traffic (e.g., thehighest utilization metric). Accordingly, during the deployment of theasymmetric network, the inclusion of one or more network links betweenthe node 1602 a and 1602 e can be prioritized over network links betweenother combinations of nodes. For example, as shown in FIG. 16B, a directoptical communication path 111 can be deployed from a high capacitytransceiver of the node 1602 a to a low capacity transceiver of the node1602 e (corresponding to the primary direction of the measured traffic).Further, another direct optical communication path 111 can be deployedfrom a high capacity transceiver of the node 1602 e to a low capacitytransceiver of the node 1602 a (corresponding to the secondary directionof the measured traffic). The high capacity transceivers and lowcapacity transceivers can be similar to or identical to those describedabove.

Further, the network traffic from the Node 1 (e.g., the node 1602 a) toa Node 3 (e.g., the node 1602 c) has the second highest ranking fromamong the groups of network traffic (e.g., the second highestutilization metric). Accordingly, during the deployment of theasymmetric network, the inclusion of one or more network links betweenthe node 1602 a and 1602 c can have the second highest priority. Forexample, as shown in FIG. 16C, a direct optical communication path 111can be deployed from a high capacity transceiver of the node 1602 a to alow capacity transceiver of the node 1602 c (corresponding to theprimary direction of the measured traffic). Further, another directoptical communication path 111 can be deployed from a high capacitytransceiver of the node 1602 c to a low capacity transceiver of the node1602 a (corresponding to the secondary direction of the measuredtraffic).

Further, the network traffic from the Node 5 (e.g., the node 1602 e) toa Node 8 (e.g., the node 1602 h) has the third highest ranking fromamong the groups of network traffic (e.g., the third highest utilizationmetric). Accordingly, during the deployment of the asymmetric network,the inclusion of one or more network links between the node 1602 e and1602 h can have the third highest priority. For example, as shown inFIG. 16D, a direct optical communication path 111 can be deployed from ahigh capacity transceiver of the node 1602 e to a low capacitytransceiver of the node 1602 h (corresponding to the primary directionof the measured traffic). Further, another direct optical communicationpath 111 can be deployed from a high capacity transceiver of the node1602 h to a low capacity transceiver of the node 1602 e (correspondingto the secondary direction of the measured traffic).

Further, the network traffic from the Node 5 (e.g., the node 1602 e) toa Node 4 (e.g., the node 1602 d) has the fourth highest ranking fromamong the groups of network traffic (e.g., the fourth highestutilization metric). Accordingly, during the deployment of theasymmetric network, the inclusion of one or more network links betweenthe node 1602 e and 1602 d can have the fourth highest priority. Forexample, as shown in FIG. 16E, a direct optical communication path 111can be deployed from a high capacity transceiver of the node 1602 e to alow capacity transceiver of the node 1602 d (corresponding to theprimary direction of the measured traffic). Further, another directoptical communication path 111 can be deployed from a high capacitytransceiver of the node 1602 d to a low capacity transceiver of the node1602 e (corresponding to the secondary direction of the measuredtraffic).

Further, the network traffic from the Node 2 (e.g., the node 1602 b) toa Node 3 (e.g., the node 1602 c) has the fifth highest ranking fromamong the groups of network traffic (e.g., the fifth highest utilizationmetric). Accordingly, during the deployment of the asymmetric network,the inclusion of one or more network links between the node 1602 b and1602 c can have the fifth highest priority. For example, as shown inFIG. 16F, a direct optical communication path 111 can be deployed from ahigh capacity transceiver of the node 1602 b to a low capacitytransceiver of the node 1602 c (corresponding to the primary directionof the measured traffic). Further, another direct optical communicationpath 111 can be deployed from a high capacity transceiver of the node1602 c to a low capacity transceiver of the node 1602 b (correspondingto the secondary direction of the measured traffic).

This process of deploying network links can continue until one or morestop criteria are met. As an example, network links can be deployeduntil a certain maximum threshold number of links have been deployed. Asan example, network links can be deployed until the measured trafficcorresponding to the deployed network links account for a certainpercentage or portion of the total network traffic. As another example,network links can be deployed until a certain amount of monetaryresources are allotted or used.

In at least some implementations, some or all of the original network1604 can be removed, decommissioned, or inactivated in favor of theasymmetric mesh network. For example, after the asymmetric mesh networkhas been deployed, at least a portion of the original network 1604 canbe removed, decommissioned, or inactivated, and the network trafficpreviously transmitted using that portion can be instead transmittedusing the asymmetric mesh network.

In the example process shown in FIG. 16F, a pair of network links isadded for each row of the table 1608 (e.g., one link in the primarydirection of the network traffic, and another link in the secondarydirection of the network traffic). However, this need not always be thecase. In some implementations, a single network link can be added foreach row of the table 1608 (e.g., in the primary direction of thenetwork traffic). In some implementations, by default, a single networklink can be added for each row of the table 1608. However, if thenetwork traffic in the secondary direction meets one or more criteria(e.g., the network traffic in the secondary direction exceeds aparticular bit rate or bandwidth), a second network link can beadditionally added in the secondary direction. This can be beneficial,for example, in reducing the time and cost associated with deployingand/or maintaining the network (e.g., as fewer network links aredeployed, and deployments are more closely targeted to areas of need inthe network).

As described above, data can be transmitted between nodes as one or moreoptical subcarriers. For instance, as described above (e.g., FIG. 4),nodes can transmit data over a transmission spectrum accommodatingmultiple different optical subcarriers, each having a correspondingfrequency or range of frequencies. In some implementations, opticalsubcarriers can be generated by modulating the output of a laser (e.g.,the laser 508 in FIG. 5).

Further, as described above, data can transmitted between network nodesthrough one or more intermediary network devices, such as networkswitches. For instance, a network switch can receive data from one node(e.g., a source node), and route the data to another node (e.g., adestination node). In some implementations, a network switch can receivedata from a source node in the form of one or more optical subcarriers(corresponding to one or more particular frequencies or ranges offrequencies, as described above), route the data to a destination nodein the form of one or more other optical subcarriers (corresponding toone or more different frequencies or ranges of frequencies, as describedabove). This sometimes may be referred to as “frequency translation” or“wavelength translation.”

To illustrate, FIG. 17A shows an example system 1700 for performingfrequency or wavelength translation. The system 1700 includes firstoptical components 1702, a Rx DSP 1704, a switch 1706, a Tx DSP 1708,and second optical components 1710. In some implementations, the firstoptical components 1702 can correspond to the Rx optics and A/D block700 (e.g., as shown in FIG. 7), the Rx DSP 1704 can correspond to theDSP 750 (e.g., as shown in FIG. 7), the Tx DSP 1708 can correspond tothe DSP 502 (e.g., as shown in FIG. 5), and/or second optical components1710 can correspond to the D/A and optics block 501 (e.g., as shown inFIG. 5). Further, the operation of one or more of the first opticalcomponents 1702, the Rx DSP 1704, the Tx DSP 1708, and the secondoptical components 1710 can be similar to or the same as itscorresponding components, as described above.

During an example operation of the system 1700, the first opticalcomponents 1702 receive data D1-D4 in the form of a first set of opticalsubcarriers SC1-SC4 (e.g., analog optical signals, corresponding to oneor more particular frequencies or ranges of frequencies f1 to f4, in asimilar manner as described above with respect to FIG. 4). The opticalcomponents 1702 convert the first set of optical subcarriers SC1-SC4into corresponding digital signals 1712 (e.g., a digitalized version ofthe first set of optical subcarriers SC1-SC4), and transmit the digitalsignals 1712 to the Rx DSP 1704. In some implementations, the opticalcomponents 1702 can include one or more laser oscillators (e.g., localoscillator lasers), optical hybrids, and/or analog to digital convertersto facilitate converting the first set of optical subcarriers SC1-SC4into corresponding digital signals 1712.

The Rx DSP 1704 generates individual digital signals 1714 a-1714 d basedon the digital signals 1712, each representing one of the data D1-D4(e.g., decoded from the optical subcarriers SC1-SC4). In someimplementations, the Rx DSP 1704 can be implemented using one or moremicroprocessors, FPGAs, or other processor circuits.

The digital signals 1714 a-1714 d are input into different respectiveinput pins of the switch 1706. In turn, the switch 1706 outputs thedigital signals 1714 a-1714 d from its output pins, where each outputpin corresponds to a different optical subcarrier that will be outputfrom the system 1700. Further, the order of the digital signals 1714a-1714 d at the input pins can be different from the order of thedigital signals 1714 a-1714 d at the output pins. Accordingly, at leastsome of the data can be input according to one optical subcarrier, andcan be output according to a different optical subcarrier. In someimplementations, the switch 1706 can be implemented using one or moremicroprocessors, FPGAs, or other processor circuits.

The outputted digital signals 1714 a-1714 d are transmitted to the TxDSP 1708. The Tx DSP 1708 generates a second set of optical subcarriersSC1-SC4 representing the information (e.g., by transmitting commandsignals 1716 to the second set of optical components 1710 specifying howthe second set of optical subcarriers SC1-SC4 are to be generated). Thegenerated second set of optical subcarriers are then output to anotherdevice (e.g., another node of a network). In some implementations, theTx DSP 1708 can be implemented using one or more microprocessors, FPGAs,or other processor circuits to facilitate generation of the commandsignals. In some implementations, the second set of optical components1710 can include on or more digital to analog converters, lasers, and/orMach-Zehnder modulators to facilitate generation of the second set ofoptical subcarriers SC1-SC4.

In some implementations, the system 1700 can generate the second set ofoptical subcarriers SC1-SC4 based on a transmitter oscillator signalprovided by a laser. In some implementations, the same laser can also beused to provide a local oscillator signal to the first opticalcomponents 1702 (e.g., to digitize the received analog signals). In someimplementations, the transmitter oscillator signal and the localoscillator signal can have the same frequency. In some implementations,a single laser can provide a single laser signal to an optical splitter.The optical splitter can split the laser signal, and provide the splitlaser signals to the first optical components 1702 (as a localoscillator signal) and the Tx DSP 1708 (as a transmitter oscillatorsignal) concurrently

In this example, the data D1-D4 is input into the system 1700 in theform of optical subcarriers SC1-SC4, respectively (corresponding to thefrequencies f1-f4, respectively). However, the data D1-D4 is output fromthe system 1700 in the form of optical subcarriers SC3, SC4, SC1, andSC2, respectively (corresponding to the frequencies f3, f4, f1, and f2,respectively). Accordingly, at least some of the data has undergone“frequency translation” or “wavelength translation” after processing bythe system 1700.

In some implementations, the switch 1706 can be dynamically reconfiguredduring operation, such that data is selectively output according todifferent optical subcarriers. For instance, the switch 1706 can receivedata at each of its input pins, and route the data from each of theinput pins to a different corresponding output pin (e.g., according to amapping between the input pins and the output pins) such that data undergoes a particular “frequency translation” or “wavelength translation.”During operation, the switch 1706 can modify the routing such that datafrom at least some of the input pins is routed to a differentcorresponding output pin (e.g., according to a modified mapping betweenthe input pins and the output pins). Accordingly, the data under goes adifferent “frequency translation” or “wavelength translation.” In someimplementations, the behavior of the switch 1706 can be control using acontrol signal (e.g., a control signal specifying the mapping betweenthe input pins and the output pins). The control signal can be providedby a control module included or otherwise associated with the system1700.

Frequency translation or wavelength translation can provide varioustechnical benefits. For instance, frequency translation or wavelengthtranslation enables nodes on a network to transmit and/or receive dataaccording to multiple different optical subcarriers (and correspondingfrequencies) as it traverses a network path from the source node to thedestination node. Accordingly, different optical subcarriers can bedynamically allocated at different legs of the network path, dependingon their availability. Further, the same optical subcarriers (andcorresponding frequencies) can be used to transmit data between nodes indifferent portions of the network, without the risk of collision.Accordingly, a limited number of optical subcarriers can be deployed tomultiple different portions of the network, without interfering with thetransmission of data.

As an example, referring back to FIGS. 11 and 12A, a first servercomputer can transmit data to a second server computer via a ToR switchthat interconnects them. In particular, the first server computergenerate a first optical subcarrier (having a corresponding firstfrequency, as described above) representing the data, and transmit thefirst optical subcarrier to the ToR switch. The ToR switch can extractthe data from the first optical subcarrier, generate a second opticalsubcarrier (and a corresponding second frequency) representing the data,where the second optical subcarrier is different from the first opticalsubcarrier (e.g., using the system 1700 shown in FIG. 17), and transmitthe second optical subcarrier to the server computer. Accordingly,although the same underlying data is transmitted first from the firstserver computer to the ToR switch, and then from the ToR switch to thesecond server computer, different optical subcarriers are used for eachsegment of the network path.

As an example, referring to FIGS. 11, 12A, and 12B, a first servercomputer coupled to a first ToR switch can transmit data to a secondserver computer coupled to a second ToR switch via a core switch thatinterconnects the two ToR switches. In particular, the first servercomputer can generate a first optical subcarrier (and a correspondingfirst frequency, as described above) representing the data, and transmitthe first optical subcarrier to the first ToR switch to which is itconnected. The first ToR switch can extract the data from the firstoptical subcarrier, generate a second optical subcarrier (and acorresponding second frequency) representing the data, where the secondoptical subcarrier is different from the first optical subcarrier (e.g.,using the system 1700 shown in FIG. 17), and transmit the second opticalsubcarrier to a core switch that interconnects the first ToR switch andthe second ToR switch. In turn, the core switch can extract the datafrom the second optical subcarrier, generate a third optical subcarrier(and a corresponding third frequency) representing the data, where thethird optical subcarrier is different from the second optical subcarrier(e.g., using the system 1700 shown in FIG. 17), and transmit the thirdoptical subcarrier to the second ToR switch. Subsequently, the secondToR switch can extract the data from the third optical subcarrier,generate a fourth optical subcarrier (and a corresponding fourthfrequency) representing the data, where the fourth optical subcarrier isdifferent from the third optical subcarrier (e.g., using the system 1700shown in FIG. 17), and transmit the fourth optical subcarrier to thesecond server computer. Accordingly, although the same underlying datais transmitted first from the first server computer to the first ToRswitch, then from the first ToR switch to the core switch, then from thecore switch to the second ToR switch, and then from the second ToRswitch to the second server computer, and then from the ToR switch tothe second server computer, different optical subcarriers are used foreach segment of the network path.

In some implementations, different optical subcarriers can be used foreach segment of a network path. In some implementations, differentoptical subcarriers can be used for some segments of a network path, andsimilar optical subcarriers can be used for some other segments of anetwork path.

In the example shown in FIG. 17A, data (e.g., data D1-D4) iscollectively input into the system 1700 in the form of a first set ofoptical subcarriers (e.g., optical subcarriers SC1-SC4), and iscollectively output according to the same set of optical subcarriers.However, this need not always be the case. For instance, in someimplemented, data can be collectively input into the system 1700 in theform of a first set of optical subcarriers, and can be collectivelyoutput according to a second set of optical subcarriers that differs, atleast in part, from the first set of optical subcarriers. For example,the second set of optical subcarriers can include one or morefrequencies that are not included in the first set of opticalsubcarriers.

To illustrate, FIG. 17B shows another example system 1750 for performingfrequency or wavelength translation. The components of the system 1750can be similar to those shown in FIG. 17A. However, in this example, thesystem 1750 includes two Tx DSPs 1708 a and 1708 b, and two secondoptical components 1710 a and 1710 b. The system 1750 can use the firstTx DSP 1708 a and second optical components 1710 a to output data usingthe same set of optical subcarriers as those that were used to input thedata (e.g., by outputting digital signals 1714 a-1714 d to the first TxDSP 1708 a to generate the optical subcarriers SC1-SC4, in a similarmanner as described above). Further, the system 1750 can use the secondTx DSP 1708 b and second optical components 1710 b to output data usinga different set of optical subcarriers than those that were used toinput the data (e.g., by outputting digital signals 1714 e-1714 h to thesecond Tx DSP 1708 b to generate the optical subcarriers SC5-SC8). Insome implementations, the switch 1706 c also can be dynamicallyreconfigured during operation, such that data is selectively outputaccording to different optical subcarriers. For instance, the switch1706 can receive data at each of its input pins, and route the data fromeach of the input pins to a different corresponding output pin (e.g.,according to a mapping between the input pins and the output pins) suchthat data under goes a particular “frequency translation” or “wavelengthtranslation.”

As described above, nodes can transmit data to one another usingtransceivers, where the transceiver one node (e.g., a “primary node”)has as higher capacity than the transceiver of another node (e.g., a“secondary node”). For example, referring to FIGS. 9A and 9B, a dataprimary node 110 can include a transceiver 900 having a first capacity,and each of the secondary nodes 112 a-112 d can include a respectivetransceiver 902 a-902 d having a second capacity. However, this need notalways be the case. For instance, in some implementations, nodes cantransmit data to one another using transceivers having equal capacities.As an example, referring to FIGS. 9A and 9B, a data primary node 110 caninclude a transceiver 900 having a certain capacity, and each of thesecondary nodes 112 a-112 d can include a respective transceiver 902a-902 d having the same capacity as that of the transceiver 900. Asanother example, some or all of the transceivers described in FIGS.10A-17B can have the same capacities as one another.

This configuration can provide certain technical benefits. As anexample, a first node can use a single transceiver to multicast data tomultiple second nodes concurrently (e.g., at a particular bit rate),rather than using a separate transceiver dedicated to each individualsecond node. Accordingly, networks can be deployed in a more costefficient manner. Further, as each of the transceivers has the samecapacity, each of the second nodes can transmit data back to the firstnode according to the same bit rate, but according to a dedicatedallotment of bandwidth.

In some implementations, a network can include several interconnectednodes. At least some of the nodes can be interconnected via linksextending between respective transceivers having equal capacities, andat least of the nodes can be interconnected via links extending betweenrespective transceivers having different capacities. The capacity ofeach transceiver (and whether there is an asymmetry in capacitiesbetween interconnected transceivers) can be selected based on theexpected flow of traffic between the nodes and/or based on an observedflow of traffic between the nodes.

Example Processes

An example process 1800 for transmitting data is shown in FIG. 18A. Insome implementations, the process 1800 can be performed by one or moreof the components of the systems described herein.

According to the process 1800, first data is transmitted from a firstnetwork switch to each of a plurality of first server computers (step1802). The first network switch includes a first transceiver. The firsttransceiver is configured to transmit data according to a first maximumthroughput. The plurality of first server computers is communicativelycoupled to the first network switch. Each first server computer includesa respective second transceiver. Each second transceiver is configuredto transmit data according to a second maximum throughput. The firstmaximum throughput is greater than the second maximum throughput.Further, the first data includes a plurality of first opticalsubcarriers. Each first optical subcarrier is associated with adifferent one of the first server computers.

Each of the first server computers receives, using a respective one ofthe second transceivers, the first data from the first network switch(step 1804).

Each of the first server computers extracts, from the first data, arespective portion of the first data addressed to the first servercomputer (1806). In some implementations, the portion of the first dataaddressed to the first server computer can be extracted by extracting aportion of the first data from the first optical subcarrier associatedwith the sever computer.

In some implementations, a second network can include a thirdtransceiver, where the third transceiver is configured to transmit dataaccording to a third maximum throughput. Further, each first networkswitch of a plurality of network switches can include a respectivefourth transceiver, where each fourth transceiver is configured totransmit data according to a fourth maximum throughput, and where thethird maximum throughput is greater than the fourth maximum throughput.The process can further include transmitting, by the second networkswitch using the fourth transceiver according to the fourth maximumthroughput, second data to each of the first network switches. Thesecond data can include a plurality of second optical subcarriers, whereeach second optical subcarrier is associated with a different one of thefirst network switches. The process can also include receiving, by theeach of the first network switches using a respective one of the fourthtransceivers, the second data from the second network switch, andextracting, by the each of the first network switches from the seconddata, a respective portion of the second data addressed to the firstnetwork switch. In some implementations, extracting the respectiveportion of the second data corresponding to the first network switch caninclude extracting a portion of the second data from the second opticalsubcarrier associated with the first network switch.

In some implementations, the second network switch can further includeone or more fifth transceivers. The method can further include comprisestransmitting, receiving or both transmitting and receiving, by thesecond network switch, third data from a wide area network using the oneor more fifth transceivers.

In some implementations, at least one of the first network switches canbe a top of rack network switch.

In some implementations, the second network switch can be a core networkswitch.

In some implementations, the process can also include transmitting, byat least one of the first server computers using the second transceiver,second data to the first network switch according to the second maximumthroughput. The second data can include a second optical subcarrier,where the second optical subcarrier is associated with the first networkswitch.

In some implementations, the first data can be transmitted using thefirst transceiver of the first network switch to each of the secondreceivers of the first server computers.

In some implementations, the second data can be transmitted using thesecond transceiver of the at least one of the first server computers tothe first transceiver of the first network switch.

Another example process 1820 for transmitting data is shown in FIG. 18B.In some implementations, the process 1820 can be performed by one ormore of the components of the systems described herein.

According to the process 1820, a plurality of network nodes areinterconnected (step 1822). Each network node includes one or morerespective first transceivers, and one or more respective secondtransceivers. Each first transceiver is configured to transmit dataaccording to a first maximum throughput. Each second transceiver isconfigured to transmit data according to a second maximum throughput.The first maximum throughput is greater than the second maximumthroughput.

A first network node from among the plurality of network nodestransmits, using a respective one of the first transceivers, first datato two or more second network nodes from among the plurality of networknodes according to the first maximum throughput (step 1824). The firstdata includes a plurality of optical subcarriers. Each opticalsubcarrier is associated with a different one of the two more othernetwork nodes.

The two or more second network nodes receive, using respective ones ofthe second transceivers, the first data from the first network node(step 1826).

In some implementations, each network node of the plurality of networknodes can be communicatively coupled to each other network node of theplurality of network nodes.

In some implementations, for each network node of the plurality ofnetwork nodes, at least one of the first transceivers of the networknode can be communicatively coupled to at least one of the secondtransceivers of each other network node of the plurality of networknodes.

In some implementations, at least one of the network nodes of theplurality of network nodes can be communicatively coupled to only asubset the other network nodes of the plurality of network nodes.

In some implementations, for each network node of the plurality ofnetwork nodes, at least one of the first transceivers of the networknode can be communicatively coupled to at least one of the secondtransceivers of only a subset of the other network nodes of theplurality of network nodes.

In some implementations, the process can also include extracting, byeach of the two more second network nodes, from the first data, aportion of the first data addressed to the that second network node.Extracting, by each of the two more second network nodes, the portion ofthe first data corresponding to the network node can include extractingthe portion of the first data from the optical subcarrier associatedwith that second network node.

In some implementations, at least some of the first transceivers of thefirst network node can be communicatively coupled to at least two of thesecond transceivers of the second network node.

In some implementations, the first data can be transmitted using thefirst transceiver of the first network node to each of the secondreceivers of the two or more second network nodes.

In some implementations, the process can further include transmitting,using the second transceiver, second data to the first network nodeaccording to the second maximum throughput. The second data can includea second optical subcarrier. The second optical subcarrier can beassociated with the first network node.

An example process 1840 for designing and deploying a network having anasymmetric mesh configuration is shown in FIG. 18C. In someimplementations, the process 1840 can be performed by one or more of thecomponents of the systems described herein.

According to the process 1840 network traffic transmitted between aplurality of network nodes via a communications network is monitored(step 1842).

Subsets of the network traffic are ranked according to one or moreranking criteria (step 1844). In some implementations, the one or moreranking criteria can include a criterion regarding a data size of thenetwork traffic transmitted between respective network nodes from amongthe plurality of network nodes, a criterion regarding a frequency bywhich the network traffic is transmitted between respective networknodes from among the plurality of network nodes, a criterion regarding adirectionality by which the network traffic is transmitted betweenrespective network nodes from among the plurality of network nodes,and/or a criterion regarding a utilization percentage of thecommunications network in transmitting the network traffic.

A mesh network is deployed between the plurality of network nodes basedon the ranking of the subsets of the network traffic (step 1844). Themesh network includes a plurality of network links. Each network linkcommunicatively couples a respective network node from among theplurality of network nodes to another respective network node from amongthe plurality of network nodes.

Deploying the mesh network between the plurality of network nodes caninclude determining, a respective rank for each of the subsets of thenetwork traffic. Each of the subsets of the network traffic can betransmitted from a respective source network node from among theplurality of network nodes to a respective destination network node fromamong the plurality of network nodes. Deploying the mesh network betweenthe plurality of network nodes can also include determining that a firstsubset of the network traffic has the highest rank from among thesubsets of the network traffic, and deploying a network link between thesource network node and the destination node corresponding to the firstsubset of the network traffic.

In some implementations, deploying the mesh network between theplurality of network nodes can include determining that a second subsetof the network traffic has the second highest rank from among thesubsets of the network traffic, and deploying a network link between thesource network node and the destination node corresponding to the secondsubset of the network traffic.

In some implementations, the process can also include transmitting oneor more optical subcarriers using the plurality of network links.

In some implementations, at least one of the network links cancommunicatively couple (i) a first transceiver of a first network nodefrom among the plurality of network nodes and (ii) a second transceiverof a second network node from among the plurality of network nodes. Thefirst transceiver can be configured to transmit data using the at leastone of the network links according to a first maximum throughput. Thesecond transceiver can be configured to transmit data according to asecond maximum throughput. The first maximum throughput can be greaterthan the second maximum throughput.

In some implementations, the mesh network can communicatively couple atleast one network node from among the plurality of network nodes to onlya subset of other network nodes from among the plurality of networknodes.

In some implementations, the process can further include removing atleast a portion of the communications network after deploying the meshnetwork.

In some implementations, deploying the mesh network can includedeploying network links between the plurality of network nodes until oneor more stop criteria are met. The one or more stop criteria a criterionthat a number of deployed network links equals to maximum number ofnetwork links, a criterion that the subsets of the network trafficassociated with the deployed network links account for a thresholdpercentage of the network traffic, and/or a criterion that an amount ofmonetary resources allotted or used to deploy the network links meets orexceeds a threshold amount.

An example process 1860 for transmitting data is shown in FIG. 18D. Insome implementations, the process 1860 can be performed by one or moreof the components of the systems described herein.

According to the process 1860, a first network node generates a firstoptical subcarrier representing first data (step 1862).

The first network node transmits the first optical subcarrier to thesecond network node (step 1864).

The second network node receives the first optical subcarrier from thefirst network node (step 1866).

The second network node generates a second optical subcarrierrepresenting the first data (step 1868). The second optical subcarrieris different from the first optical subcarrier.

The second network node transmits the second optical subcarrier to athird network node (step 1870).

In some implementations, the process can include receiving, by the thirdnetwork node, the second optical subcarrier from the second networknode, and determining, by the third network node, the first data basedon the second optical subcarrier.

In some implementations, the process can also include generating, by thesecond network node, a third optical subcarrier representing the firstdata. The third wavelength can be different from the second opticalsubcarrier. The process can also include transmitting, by second networknode, the third optical subcarrier to a fourth network node, receiving,by the fourth network node, the third optical subcarrier from the secondnetwork node, and determining, by fourth network node, the first databased on the third optical subcarrier.

In some implementations, the process can also include receiving, bythird network node, the second optical subcarrier from the secondnetwork node, and generating, by third network node, a third opticalsubcarrier representing the first data. The third optical subcarrier canbe different from the second optical subcarrier. The process can alsoinclude transmitting, by the third network node, the third opticalsubcarrier to a fourth network node, receiving, by the fourth networknode, the third optical subcarrier from the third network node, anddetermining, by the fourth network node, the first data based on thethird signal.

In some implementations, the third network node can be associated withthe second optical subcarrier. Wherein a fourth network node can beassociated with a third optical subcarrier. The third optical subcarriercan be different from the second optical subcarrier. The process canalso include further transmitting, by the second network node, thesecond optical subcarrier to the third network node and the fourthnetwork node concurrently.

In some implementations, the process can also include generating, by thesecond network node, a third optical subcarrier representing seconddata, and transmitting, by the second network node, the third opticalsubcarrier to the third network node and the fourth network nodeconcurrently.

In some implementations, the process can also include transmitting, bythe second network node, the second optical subcarrier and the thirdoptical subcarrier concurrently to each of the third network node andthe fourth network node.

In some implementations, the second optical subcarrier can betransmitted to the third network node and the fourth network node at afirst time, and the third optical subcarrier can be transmitted to thethird network node and the fourth network node at a second timedifferent from the first time.

In some implementations, the process can also include generating, by afirst laser of the first network node, the first optical subcarrier bymodulating an output of the first laser according to a first carrierfrequency.

In some implementations, the process can also include generating, by asecond laser of the second network node, the second optical subcarrierby modulating an output of the second laser according to a secondcarrier frequency.

In some implementations, the first optical subcarrier and the secondoptical subcarrier can be Nyquist subcarriers.

In some implementations, the process can also include interpreting, bythe second network node, the first optical subcarrier according to alocal oscillator signal having a first frequency. The second opticalsubcarrier can be generated according to a transmitter oscillator signalhaving a second frequency, wherein the first frequency is equal to thesecond frequency. In some implementations, the local oscillator signaland the transmitter oscillator signal can be provided by a common laser.

Example Systems

Some implementations of subject matter and operations described in thisspecification can be implemented in digital electronic circuitry, or incomputer software, firmware, or hardware, including the structuresdisclosed in this specification and their structural equivalents, or incombinations of one or more of them. For example, in someimplementations, some or all of the components described herein can beimplemented using digital electronic circuitry, or in computer software,firmware, or hardware, or in combinations of one or more of them. Inanother example, the process ###can be implemented using digitalelectronic circuitry, or in computer software, firmware, or hardware, orin combinations of one or more of them.

Some implementations described in this specification can be implementedas one or more groups or modules of digital electronic circuitry,computer software, firmware, or hardware, or in combinations of one ormore of them. Although different modules can be used, each module neednot be distinct, and multiple modules can be implemented on the samedigital electronic circuitry, computer software, firmware, or hardware,or combination thereof.

Some implementations described in this specification can be implementedas one or more computer programs, i.e., one or more modules of computerprogram instructions, encoded on computer storage medium for executionby, or to control the operation of, data processing apparatus. Acomputer storage medium can be, or can be included in, acomputer-readable storage device, a computer-readable storage substrate,a random or serial access memory array or device, or a combination ofone or more of them. Moreover, while a computer storage medium is not apropagated signal, a computer storage medium can be a source ordestination of computer program instructions encoded in an artificiallygenerated propagated signal. The computer storage medium can also be, orbe included in, one or more separate physical components or media (e.g.,multiple CDs, disks, or other storage devices).

The term “data processing apparatus” encompasses all kinds of apparatus,devices, and machines for processing data, including by way of example aprogrammable processor, a computer, a system on a chip, or multipleones, or combinations, of the foregoing. The apparatus can includespecial purpose logic circuitry, e.g., an FPGA (field programmable gatearray) or an ASIC (application specific integrated circuit). Theapparatus can also include, in addition to hardware, code that createsan execution environment for the computer program in question, e.g.,code that constitutes processor firmware, a protocol stack, a databasemanagement system, an operating system, a cross-platform runtimeenvironment, a virtual machine, or a combination of one or more of them.The apparatus and execution environment can realize various differentcomputing model infrastructures, such as web services, distributedcomputing and grid computing infrastructures.

A computer program (also known as a program, software, softwareapplication, script, or code) can be written in any form of programminglanguage, including compiled or interpreted languages, declarative orprocedural languages. A computer program may, but need not, correspondto a file in a file system. A program can be stored in a portion of afile that holds other programs or data (e.g., one or more scripts storedin a markup language document), in a single file dedicated to theprogram in question, or in multiple coordinated files (e.g., files thatstore one or more modules, sub programs, or portions of code). Acomputer program can be deployed to be executed on one computer or onmultiple computers that are located at one site or distributed acrossmultiple sites and interconnected by a communication network.

Some of the processes and logic flows described in this specificationcan be performed by one or more programmable processors executing one ormore computer programs to perform actions by operating on input data andgenerating output. The processes and logic flows can also be performedby, and apparatus can also be implemented as, special purpose logiccircuitry, e.g., an FPGA (field programmable gate array) or an ASIC(application specific integrated circuit).

Processors suitable for the execution of a computer program include, byway of example, both general and special purpose microprocessors, andprocessors of any kind of digital computer. Generally, a processor willreceive instructions and data from a read only memory or a random accessmemory or both. A computer includes a processor for performing actionsin accordance with instructions and one or more memory devices forstoring instructions and data. A computer may also include, or beoperatively coupled to receive data from or transfer data to, or both,one or more mass storage devices for storing data, e.g., magnetic,magneto optical disks, or optical disks. However, a computer need nothave such devices. Devices suitable for storing computer programinstructions and data include all forms of non-volatile memory, mediaand memory devices, including by way of example semiconductor memorydevices (e.g., EPROM, EEPROM, flash memory devices, and others),magnetic disks (e.g., internal hard disks, removable disks, and others),magneto optical disks, and CD-ROM and DVD-ROM disks. The processor andthe memory can be supplemented by, or incorporated in, special purposelogic circuitry.

A computer system may include a single computing device, or multiplecomputers that operate in proximity or generally remote from each otherand typically interact through a communication network. Examples ofcommunication networks include a local area network (“LAN”) and a widearea network (“WAN”), an inter-network (e.g., the Internet), a networkcomprising a satellite link, and peer-to-peer networks (e.g., ad hocpeer-to-peer networks). A relationship of client and server may arise byvirtue of computer programs running on the respective computers andhaving a client-server relationship to each other.

FIG. 19 shows an example computer system 1900 that includes a processor1900, a memory 1920, a storage device 1930 and an input/output device1940. Each of the components 1910, 1920, 1930 and 1940 can beinterconnected, for example, by a system bus 1950. The processor 1910 iscapable of processing instructions for execution within the system 1900.In some implementations, the processor 1910 is a single-threadedprocessor, a multi-threaded processor, or another type of processor. Theprocessor 1910 is capable of processing instructions stored in thememory 1920 or on the storage device 1930. The memory 1920 and thestorage device 1930 can store information within the system 1900.

The input/output device 1940 provides input/output operations for thesystem 1900. In some implementations, the input/output device 1940 caninclude one or more of a network interface device, e.g., an Ethernetcard, a serial communication device, e.g., an RS-232 port, and/or awireless interface device, e.g., an 802.11 card, a 3G wireless modem, a4G wireless modem, a 5G wireless modem, etc. for communicating with anetwork 1970 (e.g., via one or more network devices, such as coreswitches, ToR switches, and/or other network devices). In someimplementations, the input/output device can include driver devicesconfigured to receive input data and send output data to otherinput/output devices, e.g., keyboard, printer and display devices 1960.In some implementations, mobile computing devices, mobile communicationdevices, and other devices can be used.

While this specification contains many details, these should not beconstrued as limitations on the scope of what may be claimed, but ratheras descriptions of features specific to particular examples. Certainfeatures that are described in this specification in the context ofseparate implementations can also be combined. Conversely, variousfeatures that are described in the context of a single implementationcan also be implemented in multiple embodiments separately or in anysuitable sub-combination.

A number of implementations have been described. Nevertheless, it willbe understood that various modifications may be made without departingfrom the spirit and scope of the invention. Accordingly, otherimplementations are within the scope of the claims.

What is claimed is:
 1. A system comprising: a first network node; asecond network node communicatively coupled to the first network node;and a third network node communicatively coupled to the second networknode, wherein the first network node is configured to: generate a firstoptical subcarrier representing first data, and transmit the firstoptical subcarrier to the second network node, and wherein the secondnetwork node is configured to: receive the first optical subcarrier fromthe first network node, generate a second optical subcarrierrepresenting the first data, wherein the second optical subcarrier isdifferent from the first optical subcarrier, and transmit the secondoptical subcarrier to the third network node.
 2. The system of claim 1,wherein the third network node is configured to: receive the secondoptical subcarrier from the second network node, determine the firstdata based on the second optical subcarrier.
 3. The system of claim 1,further comprising a fourth network node communicatively coupled to thesecond network node, wherein the second network node is configured to:generate a third optical subcarrier representing the first data, whereinthe third optical subcarrier is different from the second opticalsubcarrier, and transmit the third optical subcarrier to the fourthnetwork node, and wherein the fourth network node is configured to:receive the third optical subcarrier from the second network node,determine the first data based on the third optical subcarrier.
 4. Thesystem of claim 1, further comprising a fourth network nodecommunicatively coupled to the third network node, wherein the thirdnetwork node is configured to: receive the second optical subcarrierfrom the second network node, generate a third optical subcarrierrepresenting the first data, wherein the third optical subcarrier isdifferent from the second optical subcarrier, and transmit the thirdoptical subcarrier to the fourth network node, and wherein the fourthnetwork node is configured to: receive the third optical subcarrier fromthe third network node, determine the first data based on the thirdoptical subcarrier.
 5. The system of claim 1, further comprising afourth network node communicatively coupled to the second network node,wherein the third network node is associated with the second opticalsubcarrier, wherein the fourth network node is associated with a thirdoptical subcarrier, wherein the third optical subcarrier is differentfrom the second optical subcarrier, and wherein the second network nodeis configured to transmit the second optical subcarrier to the thirdnetwork node and the fourth network node concurrently.
 6. The system ofclaim 5, wherein the second network node is configured to: generate athird optical subcarrier representing second data, and transmit thethird optical subcarrier to the third network node and the fourthnetwork node concurrently.
 7. The system of claim 6, wherein the secondnetwork node is configured to transmit the second optical subcarrier andthe third optical subcarrier concurrently to each of the third networknode and the fourth network node.
 8. The system of claim 6, wherein thesecond network node is configured to transmit the second opticalsubcarrier to the third network node and the fourth network node at afirst time, and transmit the third optical subcarrier to the thirdnetwork node and the fourth network node at a second time different fromthe first time.
 9. The system of claim 1, wherein the first network nodecomprises a first laser configured to generate the first opticalsubcarrier by modulating an output of the first laser according to afirst carrier frequency.
 10. The system of claim 9, wherein the secondnetwork node comprises a second laser configured to generate the secondoptical subcarrier by modulating an output of the second laser accordingto a second carrier frequency.
 11. The system of claim 1, wherein thefirst optical subcarrier and the second optical subcarrier are Nyquistsubcarriers.
 12. The system of claim 1, wherein the second network nodeis configured interpret the first optical subcarrier according to alocal oscillator signal having a first frequency, and generate thesecond optical subcarrier according to a transmitter oscillator signalhaving a second frequency, wherein the first frequency is equal to thesecond frequency.
 13. The system of claim 1, wherein the localoscillator signal and the transmitter oscillator signal are provided bya common laser.
 14. A method comprising: generating, by a first networknode, a first optical subcarrier representing first data; transmitting,by the first network node, the first optical subcarrier to the secondnetwork node; receiving, by the second network node, the first opticalsubcarrier from the first network node; generating, by the secondnetwork node, a second optical subcarrier representing the first data,wherein the second optical subcarrier is different from the firstoptical subcarrier; and transmitting, by the second network node, thesecond optical subcarrier to a third network node.
 15. The method ofclaim 14, further comprising: receiving, by the third network node, thesecond optical subcarrier from the second network node; and determining,by the third network node, the first data based on the second opticalsubcarrier.
 16. The method of claim 14, further comprising: generating,by the second network node, a third optical subcarrier representing thefirst data, wherein the third wavelength is different from the secondoptical subcarrier, transmitting, by second network node, the thirdoptical subcarrier to a fourth network node; receiving, by the fourthnetwork node, the third optical subcarrier from the second network node;and determining, by fourth network node, the first data based on thethird optical subcarrier.
 17. The method of claim 14, furthercomprising: receiving, by third network node, the second opticalsubcarrier from the second network node; generating, by third networknode, a third optical subcarrier representing the first data, whereinthe third optical subcarrier is different from the second opticalsubcarrier; transmitting, by the third network node, the third opticalsubcarrier to a fourth network node; receiving, by the fourth networknode, the third optical subcarrier from the third network node; anddetermining, by the fourth network node, the first data based on thethird signal.
 18. The method of claim 14, wherein the third network nodeis associated with the second optical subcarrier, and wherein a fourthnetwork node is associated with a third optical subcarrier, wherein thethird optical subcarrier is different from the second opticalsubcarrier, and wherein the method further comprises transmitting, bythe second network node, the second optical subcarrier to the thirdnetwork node and the fourth network node concurrently.
 19. The method ofclaim 18, further comprising: generating, by the second network node, athird optical subcarrier representing second data, and transmitting, bythe second network node, the third optical subcarrier to the thirdnetwork node and the fourth network node concurrently.
 20. The method ofclaim 19, further comprising: transmitting, by the second network node,the second optical subcarrier and the third optical subcarrierconcurrently to each of the third network node and the fourth networknode.
 21. The method of claim 19, wherein the second optical subcarrieris transmitted to the third network node and the fourth network node ata first time, and wherein the third optical subcarrier is transmitted tothe third network node and the fourth network node at a second timedifferent from the first time.
 22. The method of claim 14, furthercomprising: generating, by a first laser of the first network node, thefirst optical subcarrier by modulating an output of the first laseraccording to a first carrier frequency.
 23. The method of claim 22,further comprising: generating, by a second laser of the second networknode, the second optical subcarrier by modulating an output of thesecond laser according to a second carrier frequency.
 24. The method ofclaim 14, wherein the first optical subcarrier and the second opticalsubcarrier are Nyquist subcarriers.
 25. The method of claim 14, furthercomprising interpreting, by the second network node, the first opticalsubcarrier according to a local oscillator signal having a firstfrequency, and wherein the second optical subcarrier is generatedaccording to a transmitter oscillator signal having a second frequency,wherein the first frequency is equal to the second frequency.
 26. Themethod of claim 25, wherein the local oscillator signal and thetransmitter oscillator signal are provided by a common laser.
 27. A nodecomprising: a first transceiver, and a second transceiver, wherein thenode is configured to: receiving, using the first transceiver, a firstoptical subcarrier representing first data from a second nodecommunicatively coupled the node, and transmit, using the secondtransceiver, a second optical subcarrier representing the first data toa third node communicatively coupled to the node, wherein the secondoptical subcarrier is different from the first optical subcarrier.